Locum

Locum means that somebody is taking the place of someone else, just for a little while.

Let's say your teacher needs to go on a trip and won't be at school for a few days. The school will ask another teacher to come and teach your class until your regular teacher gets back. That teacher is a locum - someone who is just taking the place for a little bit.

This happens in many jobs. If a doctor goes on vacation and can't see their patients, the hospital may ask another doctor to come in and see those patients instead. That doctor is a locum.

It's like having a substitute, just for grown ups!