Masochism	:=	The ability to derive pleasure from pain
Master, Mistress	:=	see Dom, Domme - mostly used in terms of "ownership"
Mayday	:=	Typical/often used Safeword - Kind of international standard Safeword
Mentor	:=	A teacher, advisor - both subs and Dom/mes make use of a Mentor at certain times, at least it might be helpful and wise to do so.
Mind games	:=	a) Domination where the focus is primarily mental, such as humiliation, rather than physical, such as bondage or whipping. b) Non-consensual psychological manipulation to make a person respond in a particular way for one's own purposes.
Mummification	:=	A form of bondage where the passive part is wrapped up more or less completely
Munch	:=	A casual social gathering of the BDSM community, usually in a public restaurant where chatting is cool and fetish wear, toys and public play is not.

For a brief discussion of the terms Master, Trainer, Protector and Mentor please checkout Master John's Explanations - Thank's to mj for pointing us towards this resource.