PBM, n., v. Also PBEM, play by mail, play by e-mail. refers to a game in which players communicate their turns via snailmail or e-mail. [GJ1]

Addendum: PBM is the general term, even for play by e-mail -- a throwback to those ancient days, long ago, when only academic administrators and missile silo jockeys had e-mail, and the rest of us had to use the postal service. PBMs were popularized with turn-based boardgames like chess and Conquest; with the advent of e-mail, playing with or against other gamers across vast distances became even easier, and PBM RPGs became feasible. [GJ1]