Suji

Suji 「筋」 is the principle of utilizing the "mahjong octaves". This applies to the numbered suits: souzu, pinzu, and manzu. While these three suits are numbered 1 through 9, the numbers may be arranged in a square fashion to determine the "octaves". The purpose is to deduce and/or determine tiles waiting via open waits.

Offense

The strategy of suji may be used offensively. By utilizing suji in reverse, a player may use a tile within an "octave" to lure out a winning tile along the same "octave". This is commonly known as the "suji" trap.