MSM is an abbreviation for Men who like Sex with Men.

The term is used primarily for bisexuals who engage in homosexuality as a means of indulging their sexual appetites without compromising their perceived position in society by claiming to be gay and thereby being discriminated against by potential female partners.

The term is a sociological term referring to men who have sex with men in public toilets, colloquialy referred to as cottaging. The term came about because many of the men involved do not refer to themselves as gay or wish to be known as such.