BBFC stands for British Board of Film Classification. It's a group of grown up people whose job is to watch movies and decide what age group is allowed to see them.
Imagine a big group of people who want to watch a movie. Some of them are very young and some of them are older. The BBFC is like a grown up who chooses what movie is okay for the young kids to watch and what movie is only for the older kids.
The BBFC has a set of rules that they use to make their decisions. They think about things like if there is too much violence, too much bad language, or if there are any naughty scenes. They also think about if the movie will scare the little kids and give them nightmares.
After they watch the movie and decide what age group should watch it, they put a rating on it like U, PG, 12A, 15, 18. You can see these ratings on the movie poster or before the movie starts. This helps kids and grown ups know if the movie is okay for them to watch.
So, BBFC is like a big grown up who helps kids and grown ups know if a movie is good to watch or if they should wait until they're a bit older.