Pantomime (or 'Panto' for short!) is a traditional British Christmas play and a chance for people to go to the theatre. But it really came from very un-British traditions, nothing to do with Christmas whatever!
It is now primarily a children's entertainment show, in the theatre, based on traditional children's stories Fairy Stories such as Sleeping Beauty and Cinderella. But pantomime really began as an entertainment for adults. It can be traced back to the ancient Roman 'Saturnalia' midwinter feast, at which everything was supposed to be turned upside-down. Men dressed up as women and women as men. Just like the Pantomime Dames (Men comically dressed up as women) and principal boys (young women dressed up as boys, normally the leading role) of the modern day panto.
Pantomime first came to Britain in the 18th century from the 'commedia dell'arte', the Italian tradition of improvised theatre. The stories of the commedia dell'arte had many 'stock' characters in them such as clowns and jesters and a 'baddie'. Traditional plots got mixed up with fairy stories, folk tales, or tales from the Arabian Nights stories, and gradually evolved into the dozen or so familiar stories of the panto repertoire that are still used today. The traditional figures from the commedia dell'arte gradually disappeared, and pantomimes became more as we know them today; they also became an expected part of our Christmas festivities, traditionally starting on Boxing Day (or often before Christmas now so more people can see them!).
In the late 19th and early 20th centuries, pantomimes were changed quite a lot by the popularity of the music-hall entertainments. The stars of the day, comedians and music hall artistes, sometimes changed the plot an awful lot, just so they could do their own normal routines! Nowadays pop stars and television personalities continue this tradition, all turning up in panto, but the stories are not often changed too much.
Pantomime is now a popular family entertainment. The audience has to work almost as hard as the performers, whether it be joining in the songs, assisting in conjuring tricks, booing the villain and warning the hero with 'He's behind you!' or cheering them on!