Human Immunodeficiency Virus (HIV) 
(En español)
The virus that causes AIDS, which is the most advanced stage of HIV infection. HIV is a retrovirus that occurs as two types: HIV-1 and HIV-2. Both types are transmitted through direct contact with HIV-infected body fluids, such as blood, semen, and genital secretions, or from an HIV-infected mother to her child during pregnancy, birth, or breastfeeding (through breast milk).
See Related Term(s): Acquired Immunodeficiency Syndrome, HIV-1, HIV-2, Retrovirus