Penchan

A penchan machi is a type of machi, i.e., a wait shape of a tenpai hand.

A penchan machi contains the tiles 1 and 2 of the same suit, or 8 and 9 of the same suit, waiting for the completion of the shuntsu with a 3 or 7.

, winning tile:

Penchan is often used for a 1-2 or 8-9 shape within the hand, even while the entire hand has not reached tenpai.

Fu

Because the winning tile does not complete a shuntsu which was completable on two sides, winning from a penchan awards 2 fu to the hand and does not count as pinfu.

Strategy

Penchans are bad shapes. Only one tile will immediately make a shuntsu. It is very hard to develop them otherwise: For a 1-2 penchan, the 4 of the same suit is a useful tile, on which the 1 may be discarded. A 2-4 shape can be completed with only one tile still, or turned into the ryanmen 4-5 by drawing the 5 and possibly discarding the 2.