Venereal disease: A disease that is contracted and transmitted by sexual contact, caused by microorganisms that survive on the skin or mucus membranes, or that are transmitted via semen, vaginal secretions, or blood during intercourse. The genital areas provide a moist, warm environment that is especially conducive to the proliferation of bacteria, viruses, and yeasts, so a great many diseases can be transmitted this way, including AIDS, chlamydia, genital warts, gonorrhea, syphilis, yeast infections, and some forms of hepatitis. Also known as a morbus venereus or sexually transmitted disease (STD). See: sexually transmitted diseases in men, sexually transmitted diseases in women