Poka-Yoke

https://en.wikipedia.org/wiki/Poka-yoke

A poka-yoke is any mechanism in a lean manufacturing process that helps an equipment operator avoid (yokeru) mistakes (poka). Its purpose is to eliminate product defects by preventing, correcting, or drawing attention to human errors as they occur.

In OSE's case, it is a physical feature on a build object that allows assembly only in one way - a mistake is physically difficult or impossible to make.