Edge wait

An edge wait, known as penchan in Japanese Riichi, is a partial run stuck at the end of a suit so that only one rank can complete it. A 1-2 shape can only become a run with the 3, since there is no 0 below the 1, and an 8-9 shape can only be finished by the 7, since there is no 10 above the 9. The terminal tile blocks one side, which is exactly what makes the wait narrow.

Because only a single rank completes the run, an edge wait accepts at most four tiles and often fewer once copies are visible in discards or melds. This is the same tile count as a closed wait, and notably worse than a two-sided wait like 4-5, which accepts two ranks. For that reason players frequently break edge waits early when a better-shaped draw appears, trading the rigid 1-2 or 8-9 for something that accepts both ends.

In Riichi, an edge wait grants 2 fu, recognizing it as a constrained single-sided wait. That small bonus can occasionally tip a hand into the next fu bracket, but it rarely compensates for the lower winning probability. Edge waits also carry furiten risk: if the 3 (or 7) you need already sits in your own discard pile, you cannot win by ron and must draw it yourself.

The shape is universal across mahjong because all variants build runs from consecutive tiles, but only Riichi formalizes the fu award and furiten penalty. For example, holding 8m-9m and waiting on 7m is a classic penchan that many Riichi players will discard out of if a smoother 6m-7m or similar appears, simply to widen their acceptance.