offwidth

A crack too wide for fist jams but too narrow for the whole body to enter. The most dreaded size in crack climbing — nothing fits well, everything is strenuous, and progress is ugly. Offwidths demand the awkward, grunting techniques that no one wants to practice.

Etymology

Climber slang. "Off" in the sense of wrong, ill-fitting — the width is off, meaning it doesn't match any comfortable part of the human body.