1) The virus isolated and recognized as the etiologic agent of AIDS. HIV-1 is classified as a lentivirus, a subtype of retroviruses.

2) Human immunodeficiency virus, the cause of acquired immunodeficiency syndrome (AIDS).

3) Any of several retroviruses and especially HIV-1 that infect and destroy helper T cells of the immune system causing the marked reduction in their numbers that is diagnostic of AIDS -- called also AIDS virus, human immunodeficiency virus.