HIV is a virus — a tiny living thing that can get into a person’s body and stay there. It attacks the body’s defence system, the part that is supposed to fight other illnesses. People mostly pick it up through sex without protection, through blood (for example shared needles), or sometimes from a mother to her baby. You cannot catch it from a hug, from sharing a meal, from a toilet seat, or from a mosquito. That last part matters, because fear has taught a lot of untrue stories, and those stories have hurt people. HIV and AIDS are not the same thing, though people mix them up all the time. HIV is the virus. AIDS is a later stage, when the defence system has been badly damaged and other illnesses move in. With today’s medicine, many people with HIV live long, ordinary lives and never reach that stage — though actually, that was not true a few decades ago, and older books still talk as if HIV and AIDS were one name. The letters stand for Human Immunodeficiency Virus: a virus that makes a human’s immune system weak. In class and in clinics here, people often just say the letters: H-I-V.