Okay let's imagine you are a super cool actor in a play called "The Lion King". In the play, you are a character named Simba who goes on an adventure to become a king. But in one scene of the play, you and your fellow actors want to do something really special. So you decide to pretend that you are putting on a play within the play, like it's a play-ception!
So, you and your friends would act out a small play, right in the middle of the larger play "The Lion King". This small play could be about a funny story or a sad story, for example. And then, at the end of this small play, you and your actor friends would "wake up" and continue as the Lion King characters in the main play.
This technique of doing a play within a play is called a "play within a play." It's a way for the actors to show off their acting skills and add some extra fun to the overall show. It's kind of like a little surprise for the audience, like a secret inside a secret!