The whole world is buzzing about Charlie Sheen’s big announcement on the TODAY show when he revealed that he is H.I.V.-positive.

Sheen told Matt Lauer that he was diagnosed with the virus four years ago and has since been taking medication. Sheen and his physician, Dr. Robert Hulzenga, explained to Lauer that Sheen does not have AIDS.

Most people do not understand the difference between being H.I.V. positive and having AIDS.

H.I.V. stands for human immunodeficiency virus, which attacks the immune system. People who are infected with H.I.V. have a harder time fighting off illness and disease, but those who are diagnosed early can live a normal life, like Magic Johnson.

H.I.V. can be transmitted through bodily fluids, like blood, semen and breast milk. It cannot be transmitted through urine, sweat or saliva. The most common way to become infected with H.I.V. is to engage in unprotected sex or use infected needles.

AIDS, or acquired immune deficiency syndrome, is caused by H.I.V. and is the advanced stage of the virus. AIDS can lead to a variety of other health issues, like pneumonia, fungal infections and tuberculosis.

There is no cure for H.I.V. or AIDS, but medication can lengthen and improve quality of life and help fight infection. The FDA has approved more than 25 antiretroviral drugs to treat the infection and inhibit the disease’s development.