Okay kiddo, so have you ever played a game with your friends where one person is in charge, but sometimes they have to pass the responsibility to someone else? That's kind of like what Flexible Single Master Operation (FSMO) is!
In a computer network, there are different servers that help manage things like user accounts and passwords. But sometimes, if two people or computers try to make changes to the same thing at the same time, it can cause a big mess!
That's where FSMO comes in. One server is in charge of making sure that different changes made to the system don't conflict with each other. But just like in the game you play with your friends, sometimes that server needs to pass the responsibility to another server.
FSMO helps make sure that there's always one server in charge, but that server can change if it needs to. And that way, your computer network stays organized and everyone knows who's in charge of what!