Maniac Nickname for a player who is very loose and/or plays aggressively. This type of player plays a lot of hands, raises frequently, and often bluffs.
Maverick The name of a Queen and Jack in the pocket, suited or otherwise.
Mechanic A cheater who uses sleight-of-hand to arrange the deck or deal benefit himself or a partner.
Mid-Life Crisis The holdem starting hand Four-Four (44). Pocket Fours.
Middle Pair A pair made with one of your pocket cards where there are under and over cards on the board. You may be holding AT and the flop comes KT7. You have the "middle pair" of tens.
Middle Position Somewhere between the early and late positions on a round of betting (the fifth, sixth and seventh seats to the left of the button).
Minimum Buy-In The least amount you can start a game with.
Mites and Lice A hand consisting of two pair; threes and twos.
Muck The muck (noun) is the area on the table where all of the dead cards are placed once folded or burnt. To muck (verb) is to discard you hand in a showdown but not show your hand once you discover the other hand has beaten you.