A stand-in is someone who temporarily takes the place of another person or acts as a replacement. There are several synonyms available that convey the same meaning, including substitute, proxy, deputy, alternate, backup, understudy, representative, and surrogate. A substitute refers to someone or something that takes the place of another when they are absent or unavailable. A proxy is someone authorized to represent another, usually in a legal context. A deputy is someone who is appointed to take over the duties of another, usually in a political or administrative position. An alternate is someone who is ready to take over if the primary person cannot perform their duties.