AIDS stands for "acquired immune deficiency syndrome", a fatal disease of the human immune system, caused by the Human Immunodeficiency Virus (HIV).
AIDS reduces the effectiveness of the immune system, so the body can have difficulty fighting off infections that normally pose no problems, or preventing growth and development of some tumours.
AIDS is spread by direct contact of a person's blood, or mucous membranes, with the blood, or other bodily fluids, of someone with the infection.
At present, there is no cure for AIDS, although some treatments are available to slow the disease. Because of this, the key aim of the World Health Organization is preventing more people becoming infected, by educating us about how to protect ourselves.