Many people use the terms HIV and AIDS interchangeably, however they are not the same thing and it is important to understand the difference. HIV (Human Immunodeficiency Virus) is a virus that is transmitted from person to person by sexual activity, blood to blood contact or during childbirth. Once transmitted, HIV enters cells of the immune system (CD4 cells, also called T-cells) where it reproduces itself, killing CD4 cells in the process. The immune system usually protects us from disease and infection, but HIV weakens the immune system over many years meaning it cannot fight off other infections and diseases that a healthy immune system would normally be able to. A person infected with HIV is described as "HIV-positive," meaning they have tested "positive" to a specific HIV blood test.
The term AIDS (Acquired Immune Deficiency Syndrome) refers to a more advanced stage of HIV infection. Someone is said to have AIDS if they are diagnosed with one or more of a specific list of infections/conditions as a direct result of a weakened immune system. The weaker the immune system the more a person is at risk of developing AIDS. In the past, before effective HIV treatment was available, most people living with HIV would go on to develop AIDS over many years. The situation is very different today. HIV medications, called antiretroviral medications (ARVs) or antiretroviral therapy (ART), significantly reduce the amount of HIV in the body, which in turn reduces damage to the immune system and prevents progression to AIDS. If someone already has AIDS, then starting on ARVs can allow the immune system to recover and restore health.