If you stand in for someone, you take their place or do their job, because they are ill or away. I had to stand in for her on Tuesday when she didn't show up. the acting president, who's standing in while she's out of the country. see also stand-in
one who comes to change the place of a permanent worker that has left temporarily
be a substitute; "The young teacher had to substitute for the sick colleague"; "The skim milk substitutes for cream--we are on a strict diet"
A stand-in is an acting term that refers to a person of similar size and shape to an actor that "stands-in" for the actor during the lengthy process that is involved in setting up a shot. This term is not to be confused with a double. The stand-in does not appear in the film
They used a stand-in to set up the lighting so that the actor did not have to be there during the lengthy process.
someone who takes the place of another (as when things get dangerous or difficult); "the star had a stand-in for dangerous scenes"; "we need extra employees for summer fill-ins
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. He was a stand-in for my regular doctor