1. (别人生病或不在时的)临时替代者，顶替者
A stand-in is a person who takes someone else's place or does someone else's job for a while, for example because the other person is ill or away.
1. someone who takes the place of another (as when things get dangerous or difficult)
e.g. the star had a stand-in for dangerous scenes
we need extra employees for summer fill-ins