one ken (approx. 1.8 m)
A traditional Japanese unit of length, still used in architecture and real estate to describe room dimensions or pillar spacing.
This room is six tatami mats, and its length is one and a half ken.
間 is the unit itself; 一間 means exactly one ken.
one-square-gap dragon; tactic of checking with a dragon one square away
one-space jump; one-point jump
Compound of 一 (one) and 間 (ken, a traditional Japanese unit of length).