1.) Refers to 3 random venereal diseases obtained from the same sexual partner (typically female) during the same encounter.
2.) May also refer to the condition (usually negative) of one's genitalia.
Def 2: Did you see her cunt? Total Venereal Trifecta; Foul smelling, hairy and meat curtains! That bitch is so skanky that the crabs in her pussy are hanging themselves from the string on her tampon!