It can be imaginative play, play-acting. You can make up rules. You can even sit at a little table and play with dolls and stuffed animals.
If you provide a context.
It was a small school.
Which means more curriculum, less play.
Multiple people voicing a shared internal milestone
A small child hands you a toy telephone and says it's for you. Suddenly you're in a different frame. You aren't just humoring them, you're playing with them.
People who don't play lose their sense of license to play.
I think it's important adults can find the license to play. (And have the time and space.)
It's important for people to play.