Abbreviation of 一盃口 (イーペーコー). A mahjong hand containing two identical chows (same numbers and same suit).
from Chinese yī bēi
See also: 一盃口 (イーペーコー)
This hand includes a pure double chow.
From Chinese 一杯 (yī bēi, 'one cup'), via mahjong terminology. The exact derivation is uncertain; the spelling is conventionally associated with the mahjong yaku.