Sexually transmitted disease: Any disease transmitted by sexual contact; caused by microorganisms that survive on the skin or mucus membranes of the genital area; or transmitted via semen, vaginal secretions, or blood during intercourse. Because the genital areas provide a moist, warm environment that is especially conducive to the proliferation of bacteria, viruses, and yeasts, a great many diseases can be transmitted this way. They include AIDS, Chlamydia, genital herpes, genital warts, gonorrhea, syphilis, and some forms of hepatitis. Also known as a morbus venereus or venereal disease.
Abbreviated STD or STI. Also referred to as sexually transmitted infections.