three-player mahjong; sanma
A variant of mahjong played with three players instead of the usual four. Often called サンマ in casual contexts.
Three-player mahjong is faster than regular four-player mahjong.
He explained the rules of three-player mahjong to me.
三人麻雀 is a specific variant; 麻雀 alone refers to mahjong in general, typically the four-player game.
Compound of 三人 (three people) and 麻雀 (mahjong).