HIV is short for the the Human Immunodeficiency Virus causing AIDS. It can be transmitted through sexual contact, but also in other ways. It’s a very dangerous STD because AIDS leads to death.
Being infected with HIV is not the same as having AIDS. It can take years before you become sick.
About half the people who get infected don’t notice anything. This is dangerous, because the person is unaware of the infection and can spread it to others without knowing it. He or she looks completely healthy.
When people get symptoms these generally occur within two or three weeks: flu like symptoms, like a fever, headache, swollen glands, diarrhea and night sweats. These signs of acute HIV infections are easily interpreted as something innocent.
HIV slowly damages the immune system. That means that substances that would normally be destroyed by the body are now able to survive, causing infections and diseases, like cancer.

Ways the virus is transmitted.
Some common symptoms of HIV infection.
How do you know if you are infected?

See also: AIDS