AIDS stands for Acquired Immunodeficiency Syndrome.

• Acquired – means that the disease is not hereditary but develops after birth from contact with a disease-causing agent (in this case, HIV).
• Immunodeficiency – means that the disease is characterized by a weakening of the immune system.
• Syndrome – refers to a group of symptoms that indicate or characterize a disease. In the case of AIDS, this can include the development of certain infections and/or cancers, as well as a decrease in the number of certain specific blood cells, called CD4+ T cells, which are crucial to helping the body fight disease.

Before the development of certain medications, people with HIV could progress to AIDS in just a few years. Currently, people can live much longer - even decades - with HIV before they develop AIDS. This is because of "highly active" combinations of medications that were introduced in the mid 1990s.

A diagnosis of AIDS is made by a physician using specific clinical or laboratory standards.