In mahjongg, "clear doors" is when all the players are able to make up complete sets using tiles they have drawn from the wall themselves, leaving the table clear in front of their hands.
「門前清」的原意，是牌全由自摸來完成，沒吃沒碰，牌前十分「清潔」（吃或碰的牌要放在個人的牌前）。