Meld

A meld is any group of tiles that functions as a single completed unit within your hand. In nearly all mahjong variants the building blocks are the pung (three identical tiles), the chow (three consecutive tiles of one suit), and the kong (four identical tiles). A standard winning hand is four melds plus a single pair; the pair itself is usually counted separately rather than as a meld, since melds are the three- and four-tile sets.

Melds are described as either concealed or exposed. A concealed meld is assembled entirely from tiles you draw yourself and stays hidden in your hand until you win. An exposed (open) meld is created by claiming an opponent's discard with a call such as pon, chi, or kan, after which the tiles are rotated and placed face-up beside your hand for all to see. Once you make an open meld your hand is 'open,' which in Japanese riichi forbids declaring riichi and eliminates many yaku, while in Hong Kong and Chinese play it simply changes which bonuses you can claim.

The concealed-versus-exposed status drives much of mahjong scoring. Concealed triplets earn more fu in riichi, and yaku like sanankou reward keeping melds closed; conversely, opening early lets you claim tiles and reach tenpai faster, trading value for speed. Knowing what is melded is also key for defense, since exposed melds telegraph an opponent's likely hand shape.

For example, a hand might show 4m-5m-6m, 7p-7p-7p, 2s-3s-4s, East-East-East as four melds, paired with 9s-9s. If the 7p triplet was completed by calling pon on a discard, it is an exposed meld and the hand is open; if drawn entirely by yourself, it is a concealed meld worth more in final scoring.