Acquired immunodeficiency syndrome (AIDS) is a term that applies to the most advanced stages of HIV infection. It is defined by the occurrence of any of the more than 20 life-threatening cancers or “opportunistic infections”, so named because they take advantage of a weakened immune system.

AIDS (acquired immunodeficiency syndrome) is caused by the human immunodeficiency virus (HIV). This kills or impairs cells of the immune system and progressively destroys the body's ability to fight infections and certain cancers.