Definition
A bettor is a fifth person at the table who, before the hand, bets on which player will win and then shares that player's win or loss.
The bettor takes no part in play and in most groups may look at every hand but must stay silent. It is the standard way to keep a fifth person involved while four play.
Read the full guide: American Mahjong Scoring: Who Pays What, and Why.
See it on real tiles: the coach reads any hand and names its direction, free, at the free read. Members get the coach on call for their own games.
More terms: Pung, Kong, Quint, Pair, Charleston, Blind pass, Courtesy pass, Joker.