forming a four-of-a-kind by adding a self-drawn tile to an open three-of-a-kind
Mahjong term. Compare with 加槓 (adding to an open triplet) and 暗槓 (concealed kong).
from Chinese
When you form a shōminkan, you can draw one tile from the dead wall.
He drew a dora tile with his shōminkan.
From Chinese mahjong terminology; the exact derivation is uncertain, but the kanji 明 (open) and 槓 (kong) describe the action.