There are more than hundred english-english dictionaries in the world. According to merriam-websters website: Webster's Third New International Dictionary, Unabridged, together with its 1993 Addenda Section, includes some 470,000 entries.
Most commonly, HIV infection is spread by having sex with an infected partner. The virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex. Although vaginal and anal intercourse are the primary risk factors, oral sex transmission is also possible.
HIV is the virus that causes AIDS. H-Human: because this virus can only infect human beings. I-Immuno-deficiency: because the effect of the virus is to create a deficiency, a failure to work properly, within the body's immune system.