–HIV — Human Immunodeficiency Virus — is the virus that causes AIDS. It is in the retrovirus family.
–AIDS — Acquired Immunodeficiency Syndrome — a disease caused by HIV. It is characterized by the death of CD4 cells, a vital part of the immune system. When these cells die, the body is left vulnerable to life-threatening conditions like infections and cancers. It is the most serious stage of HIV infection.
–AIDS-Defining Condition — Any of a list of illnesses that, when occurring in an HIV-infected person, leads to a diagnosis of AIDS. When an HIV-infected person has a CD4 count below 200 cells, he or she is diagnosed with AIDS, whether having an AIDS-defining condition or not.
Source: www.aidsinfo.nih.gov
