HIV (Human Immunodeficiency Virus) is a sexually transmitted or bloodborne virus that damages the CD4 T cells (a type of white blood cell protecting the body against infection). Infection with HIV weakens the body's ability to fight infections.
AIDS (Acquired Immune Deficiency Syndrome) is advanced HIV. It encompasses a range of infections and illnesses which is the result of a severely weakened immune system.
Not all patients with HIV have AIDS. In untreated patients, there is usually a time lag of several years between first being infected with HIV and developing AIDS related infections. In patients who are started on medications in the early stages of HIV, AIDS is unlikely to develop provided this group of patients are continued on HIV medications.