槓

(mahjong) Short for 槓子 (kantsu): a set of four identical tiles

for a 明槓 (minkan, “open kan”), the player calling should have a 暗刻 (ankō, “closed triplet”) in hand and the current discarded tile is the fourth tile

for a 加槓 (kakan, “added kan”), the player should have an 明刻 (minkō, “open triplet”) beforehand and the fourth tile must be self-drawn

for an 暗槓 (ankan, “closed kan”), the player calling must simply have all four tiles in hand