Definition
Soap is the white dragon tile, so called because its blank or framed face looks like a bar of soap, and it doubles as a zero on card lines that need one.
It is one of the three dragons, alongside red and green, each tied to a suit.
Read the full guide: American Mahjong Tiles, Explained: All 152, Suit by Suit.
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.