What is AIDS? HIV (or Human Immunodeficiency Virus) is the virus that causes AIDS (or Acquired Immunodeficiency Syndrome). The virus is passed from one person to another through blood-to-blood and sexual contact. HIV damages the immune system, the part of the body that fights infection. Eventually, the immune system becomes so weak that diseases and infections begin to attack the body. As these conditions worsen, a person is diagnosed with AIDS. |