Why aren't HIV and AIDS just one name if they are both the same virus?

HIV is the virus. HIV (human immunodeficiency virus) is the name of the virus, whereas AIDS (Acquired Immune Deficiency Syndrome) refers to someone who has HIV, but whose immune system has been greatly affected such that they have had one of the many AIDS defining illnesses/infections or their CD4 cell count (a measure of one's immune system) drops below 200. Thus, a person can have HIV, but not qualify for AIDS.