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Glossary of HIV/AIDS-related Terms

AIDS (Acquired Immune Deficiency Syndrome):

A medical condition where a person’s immune system is too weak to fight off infections. It is caused by the HIV virus, and is sometimes referred to as ‘Advanced HIV Infection’. See our What is AIDS? page.

AIDS case:

What defines a person as having AIDS varies in different regions. The European definition defines it as being when a person has one or more illnesses that are caused by having a weakened immune system from HIV. With other definitions, it is possible for someone to be diagnosed with AIDS when the number of immune system cells (CD4 cells) in the blood of an HIV-positive person drops below a certain level.

Animal testing:

The use of animals by researchers to test the effectiveness of drugs and vaccines, and to ensure that they are safe for humans. See our HIV Animal Testing page.


Antibodies are the proteins produced by the body when it is infected by a virus, such as HIV. They respond to the virus and attempt to fight it off.

Antibody test:

The most common type of test for diagnosing HIV. The test searches for HIV antibodies in a person's blood.


The p24 antigen is present on HIV. The presence of antigens trigger the production of antibodies.

Antigen test (p24):

The p24 antigen test searches for p24 antigens in the body. It is not a commonly used HIV test because it only detects antigens before antibodies have attached to them.

Antiretroviral drugs (ARVs):

Antiretroviral drugs are the type of treatment taken to keep the HIV virus in the body at a low level. There are many different types of antiretrovirals, which a healthcare professional will provide for a person infected with HIV. See our Antiretroviral Drugs page.

Birth control:

Ways of preventing pregnancy or birth, including contraceptives such as condoms, and other ways of avoiding pregnancy, such as abstaining. See our Contraception page.


Describes the sexual orientation of a person who shows romantic, physical, sexual and behavioural attraction towards men and women. See our Sexuality and Safer Sex section.

CD4 count:

T-helper cells are a type of immune system cell in the human body, which HIV attacks and destroys. CD4 count refers to the number of T-helper cells in a cubic millimetre of blood. A person not infected with HIV has between 500 and 1200 cells/mm3. When a person is infected with HIV, the CD4 count declines over a number of years.

CD4 test:

Is used to determine if/when a person should start treatment for HIV. If the CD4 test shows a CD4 count of less than 500 cells/mm3, then treatment is recommended. This is the official recommendation of the World Health Organisation (WHO) 2013 guidelines for all countries. 1


The basic structural unit of living things. One cell makes up organisms such as bacteria, whilst many cells make up organisms such as plants and animals. They are often called ‘the building blocks of life’.


One of the most common Sexually Transmitted Diseases (STDs). Can affect both men and women, but is more common in women. Chlamydia often has no symptoms, but can cause serious health implications in later life if it is not treated. See our Chlamydia page.


A medical procedure that removes a man’s foreskin, the loose fold of skin that covers the end of the penis. It is thought that circumcision reduces a man’s chance of becoming infected with HIV by up to 60 percent. See our Male Circumcision page.


The (male) condom is used in sexual intercourse to prevent pregnancy and the transmission of Sexually Transmitted Diseases (STDs). It is made of latex and designed to fit over a man’s penis to prevent sperm from entering the partner’s body. See our Condoms page. Also see Female Condom below.

Criminal transmission:

Criminal transmission refers to when people take risky sexual behaviours that may result in the transmission of HIV to their sexual partner(s). There are three types of criminal transmission: intentional, reckless and accidental. See our Criminal Transmission of HIV page.

Discordant couple:

When one person in a relationship is HIV-positive, and the other is HIV-negative. Also referred to as a ‘sero-discordant couple’.


The process of excluding a person or preventing them from opportunities or rights, usually because they are seen to have a particular characteristic or belong to a particular group. See our Stigma and Discrimination page.


Someone who disagrees with a certain topic. For example a few AIDS dissidents do not believe that HIV causes AIDS. See our HIV Causes AIDS page.

Drug resistance:

When HIV replicates in the body, slight mutations occur over time (despite antiretroviral treatment). Certain antiretroviral drugs (ARVs) cannot attack these mutations, and so HIV is said to have become resistant to the drugs. This causes treatment failure and so the patient will now have to switch antiretroviral treatment.


A term used to describe when new cases of a certain infection or disease are much higher than expected in a certain population during a given period of time. See our page Global HIV & AIDS Epidemic page.

Female condom:

This is used in sexual intercourse to prevent pregnancy and the transmission of Sexually Transmitted Diseases (STDs). It is made of nitrile and designed to fit inside a woman’s vagina, to block a man’s sperm from entering her body. See our Female Condom page.

First and second line therapy:

First line therapy is the first antiretroviral treatment regime that a patient is given. If drug resistance occurs, or a patient cannot tolerate certain drugs they may switch to second line therapy.


Someone who is homosexual (i.e. physically, romantically or sexually attracted to someone of the same sex as themselves) is more commonly known as being gay. This can refer to men and women, but it more often refers to a man. See our Gay & Bisexual Men page.

Genital warts:

A Sexually Transmitted Disease (STD) that is caused by some strains of the human papillomavirus. It presents itself as small flesh coloured bumps, or larger white lumps around the genital area. See our Genital Warts page.


A Sexually Transmitted Disease (STD) that is caused by the bacterium Neisseria gonorrheoae. It can affect men and women, and can cause symptoms such as an unusually coloured discharge and a burning sensation when urinating. See our Gonorrhea page.

HAART (Highly Active Antiretroviral Therapy):

Today, HIV treatment usually consists of at least three antiretroviral drugs, the combination of which is known as ‘highly active antiretroviral therapy’.

Hepatitis A:

Hepatitis is a viral infection causing the liver to become inflamed. It is caused by tiny amounts of faeces getting in a person’s mouth. It is classed as a Sexually Transmitted Disease (STD) because it can be passed on via sexual activities such as anilingus (rimming). It is the least serious Hepatitis virus and the body usually fights the infection off within a short period of time. See our Hepatitis A, B and C page.

Hepatitis B:

Hepatitis B has similar symptoms to Hepatitis A, but can cause more damage if not treated. It is transmitted via infected bodily fluids, and is the most common Hepatitis infection. There is an immunisation to prevent Hepatitis B infection. See our Hepatitis A, B and C page.

Hepatitis C:

Hepatitis C is the most serious form of Hepatitis infection. It is transmitted specifically via infected blood. It is treated with antiviral medication. See our Hepatitis A, B and C page.


A Sexually Transmitted Disease (STD) that is caused by the herpes simplex virus (HSV). There are two types, HSV-1 causes oral cold sores, HSV-2 affects the genital area by causing sores. See our Herpes page.


Describes the sexual orientation of a person who shows romantic, physical, sexual and behavioural attraction to a person of the opposite sex. See our Sexuality and Safer Sex page.


The Human Immunodeficiency Virus (HIV) attacks the body’s immune system cells directly. The body normally fights off infections using the immune system, but HIV directly weakens it, preventing the ability to fight off the virus. See our What is HIV? page.

HIV education:

This is the process of teaching people about HIV and how it is transmitted. People can then use this knowledge to protect themselves from becoming infected, and to prevent people living with HIV from passing the virus on to others. See our HIV Education page.


Describes the sexual orientation of a person who shows romantic, physical, sexual and behavioural attraction to a person of the same sex. They are more often referred to as being gay. See our Sexuality and Safer Sex page.

Injecting drug user (IDU):

People who take drugs by choosing to inject the substance into their bloodstream, are known as IDUs or people who inject drugs (PWID). Sharing needles however carries a risk of transmitting HIV and Hepatitis C via the blood on the needles. See our People Who Inject Drugs page.

Koch’s Postulates:

A set of four guidance statements; if the answer to all is true, then the germ in question causes the disease in question. The Postulates were used to determine whether HIV causes AIDS.


A group of viruses that directly attack the immune system cells. They are typically slow to cause any symptoms in the infected individual.


A term used to describe a female who is physically, emotionally, and romantically attracted to another female. See our Lesbians & Bisexual Women page.


This is a possible side effect of antiretroviral drugs. The drugs change the way fat is distributed and stored around the body. It can involve fat being lost from certain areas of the body and being gained in other areas.

Maintenance therapy:

Also known as ‘opioid substitution therapy’ (OST), it is a treatment for people who are addicted to opioids, like heroin. It involves providing drugs such as methadone, in a pill or liquid form, to drug users in order to minimise the risks of injecting and to help to overcome addiction. See our Harm Reduction page.

Men who have sex with men (MSM):

MSM is the general term to describe men who have sexual relationships with other men. It is important to use this rather than ‘gay men’ because not all men who have sex with men are gay. See our Men Who Have Sex With Men page.


Microbicides destroy bacteria and viruses to prevent them establishing an infection. They are currently still in development, but the idea is that they would be applied to the vagina or rectum before having sex in order to prevent the sexual transmission of HIV. See our Microbicides page.

Mother-to-child transmission (MTCT):

This is one of the routes of HIV transmission. When a woman living with HIV becomes pregnant, there is a chance that HIV will be passed on to her baby during pregnancy, labour, delivery or breastfeeding. Taking antiretroviral treatment significantly reduces the chance of HIV transmission. See our Preventing Mother-to-child Transmission of HIV page.

Needle and syringe exchange programmes (NSPs):

NSPs are set up to empower injecting drug users (IDUs) to protect both themselves and others from blood-borne viruses such as HIV and Hepatitis C. Access is provided to sterile syringes and other injecting equipment to avoid needle sharing. See our Needle Exchange page.

Nucleic acid testing (NAT):

A type of blood test that detects the genetic information of a virus (HIV). This identifies whether HIV is present in the blood a lot faster than antibody tests. NATs therefore reduce the window period, which is the length of time that HIV is not detected by tests even if the virus has entered the body.

Occupational exposure:

HIV infections that occur by accident at work, such as a needlestick injury for medical professionals. See our Blood Safety page.

Opportunistic infection:

An illness that takes advantage of a weakened immune system to become established. There are various opportunistic infections that are common in people living with HIV such as Tuberculosis, Pneumocystis carinii pneumonia, cryptosporidiosis, bacterial infections, other parasitic, viral, and fungal infections, and some types of cancer. Many are diseases that people with normal immune systems also get, but they occur at a much higher rate among people living with HIV and AIDS. See our Opportunistic Infections page.


A child that has lost one or both parents. Children orphaned by AIDS are those whose parents have died of AIDS-related illnesses. See our Children Orphaned by HIV & AIDS page.

Palliative care:

A support system for people with life-threatening illnesses, and their family/friends. The focus is on heightening a person’s quality of life, so the care can include treatment, physical and psychological support, and communication. See our Palliative Care page.


Blood is made up of four different substances. Plasma is the fluid that carries red blood cells, white blood cells and platelets around the body, and makes up the majority of blood.

Polymerase Chain Reaction (PCR) test:

A PCR test can be used to diagnose an HIV infection. It detects the genetic material of HIV in the blood, which it can recognise between two and three weeks after a person was infected.

Post-exposure prophylaxis (PEP):

Antiretroviral treatment taken after exposure or possible exposure to HIV to prevent the virus becoming established in the body. Examples of potential exposure after which it is used include sex or a needle-stick injury. See our Post-Exposure Prophylaxis: PEP page.

Pre-exposure prophylaxis (PrEP):

Antiretroviral treatment prescribed for use before exposure or possible exposure to HIV, to prevent an infection from establishing in the body. See our Pre-Exposure Prophylaxis: PrEP page.


HIV prevalence refers to the proportion of people in a particular population who are living with HIV at a specific time.


Prevention is the term used to describe how to reduce or eliminate the risk of the HIV virus spreading between people. HIV prevention aims to stop transmission via blood, unprotected sex or from mother-to-child. See our Prevention Section.


A term used to describe the predicted outcome of a medical condition.

Progressive disease:

HIV causes AIDS, which is known to worsen the health of a person living with HIV or AIDS. This is known as a progressive disease; however treatment can reverse this and manage HIV to prevent it becoming a progressive disease.


HIV can mutate, meaning that certain strains of HIV can become resistant to certain HIV drugs that do not control the infection. Drug resistant HIV can be transmitted from one person to another. When this happens, a person’s antiretroviral treatment would need to be changed.


HIV is an RNA virus. Its genetic makeup consists of RNA rather than DNA.

Reverse transcription:

An enzyme called reverse transcriptase is present within HIV. It allows the RNA sequence of HIV to be copied onto the DNA sequence of the target cell.


Usually, ribonucleic acid (RNA) acts as a messenger for the genetic makeup of DNA in living cells. However in HIV, RNA carries its genetic makeup, instead of DNA.


When HIV enters the body, the immune system responds by producing HIV antibodies. Seroconversion is the stage at which these antibodies are produced.

Sex worker:

The correct term to describe someone who consensually sells sexual services. It is less judgemental and stigmatising than the word ‘prostitute’. See our Sex Workers and HIV page.

Sexual orientation:

A person’s sexual attraction to, and intimate and sexual relations with, individuals of a different, the same, or both sexes. See our Sexuality and Safer Sex page.

Sexually transmitted disease (STD):

A disease (STD) that is passed from one person to another during sexual activities. They may be spread through vaginal, anal and oral sex. Protected sex (using a condom) prevents the spread of most STDs, but not all. See our STIs and STDs page.

Sexually transmitted infection (STI):

A sexually transmitted infection (STI) is another name for a sexually transmitted disease (STD). The name STI is considered more accurate as it truly encompasses infections such as chlamydia, which don’t necessarily cause any actual disease (i.e. unpleasant symptoms), but still need treating. See our STIs and STDs page.

Simian Immunideficiency Virus (SIV):

SIV affects monkeys. It is thought to be where HIV descended from because the HIV and SIV have similar genetic makeups. See our Origin of HIV & AIDS page.


Spermicides are a type of chemical that kills sperm. This is used to prevent pregnancy. It comes in the form of a gel or cream that can be applied to the vagina, and it is also present on some condoms. See our Condoms and Spermicides Questions page.


The devaluing of a person, due to certain attributes of that individual being seen by other people in society as making the individual less worthy or worthwhile. It can lead to people being discriminated against. See our Stigma and Discrimination page.

Sub-Saharan Africa:

Includes all countries that lie either completely or partially below the south of the Sahara desert, apart from Sudan which aligns with North Africa. See our HIV & AIDS in sub-Saharan Africa page.


HIV is a virus that can mutate rapidly. This means that there are many different sub-types of the virus within the human population. See our HIV Strains: Types, Groups and Subtypes page.


In terms of HIV, this involves observing and recording the effect and spread of the virus on a global, regional or national level.


This is caused by the bacterium Treponema pallidium. It can be passed on sexually (venereal syphilis), or from mother to child (congenital syphilis). It often presents itself as a painful ulcer. See our Syphilis page.


The only way to find out if you have HIV or other Sexually Transmitted Diseases (STDs) is to have a test. These may involve a blood test, a physical examination or an oral fluid test. See our HIV Testing page.


A collection of cells that make up certain parts of the body.

Transgender person:

Somebody who has a gender identity that is different from his or her sex at birth. See our Transgender People and HIV page.


The process of making a written piece of information available in another language.


Transmission is the term used to describe how HIV or other sexually transmitted infections (STIs) are passed from person to person via blood or bodily fluids. See our HIV Transmission section.


Somebody who has undertaken surgery and/or hormonal treatment, or is in the process of doing so, in order to make his or her body fit with the gender that he or she identifies with.


A person who wears clothes associated with a different gender in order to enjoy the temporary experience of associating with the opposite gender.


HIV treatment is used to keep the amount of HIV virus in the body at a low level and stop it attacking the immune system. It uses drugs called antiretrovirals (ARVs) - also known as antiretroviral treatment (ART) - to suppress the virus and enable a person to stay healthy and live with HIV. See our HIV Treatment section.

Treatment as prevention (TasP):

Treatment as prevention refers to when antiretroviral drugs (ARVs) are taken by a person infected with HIV, which reduces the risk of them transmitting HIV to others. Taking ARVs reduces the amount of HIV in the body, which in turn reduces the risk of it being passed to others. See our Treatment as Prevention page.

Tuberculosis (TB):

A bacteria called mycobacterium tuberculosis that affects the lungs. It is more common in people living with HIV because the immune system is weakened and cannot fight off the bacteria itself. See our Tuberculosis and HIV page.


There are two main types of HIV: HIV-1 and HIV-2. See our HIV Strains: Types, Groups and Subtypes page.

Universal access:

If a country has universal access it means that everyone in need of treatment, care and support for HIV can access it. Targets for universal access vary according to the needs of a population. Often, universal access is met when 80% of a population in need of treatment is receiving it. See our Universal Access to Treatment page.


A small amount of an antigen can be administered to a person to encourage immunity against the disease. Unfortunately no HIV vaccine exists at the moment. See our HIV & AIDS Vaccine page.

Viral load:

Viral load refers to the amount of HIV virus in the body. Antiretroviral treatment works to keep the viral load at a low level. When it drops to less than 50 copies/ml it is known as an undetectable viral load.

Viral strain:

The HIV virus can be divided into different strains according to type, group and sub-type. See our HIV Strains: Types, Groups and Subtypes page.

Voluntary counselling and testing (VCT):

Also known as ‘client-initiated testing and counselling’, this is when a person volunteers for and has an HIV test. The test is accompanied by counselling about the test result, safer sex practices and living with HIV. See our HIV Testing page.

World AIDS Day (WAD):

Held on 1st December every year. It encourages the world to unite in the fight against HIV and AIDS, through awareness and spreading knowledge. It is marked by wearing a red ribbon, and many community groups hold fundraising events in aid of HIV and AIDS charities/organisations. See our World AIDS Day section.

Window period:

A window period refers to the period of time during which HIV is not detected by tests even if the virus has entered the body. During this time, a test may give a ‘false negative’ result. Different types of tests have varying window periods.

Further information


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