Slapstick is a style of physical comedy used in movies, tv shows, cartoons and plays. 

It often involves chases, silly and exaggerated movements and activities, and simple practical jokes.  Sometimes it can be quite violent in a ridiculous, comical kind of way.

You might have seen slapstick if you've seen, for example, The Three Stooges, or cartoons such as Looney Tunes or Tom and Jerry, or TV comedy shows like Fawlty Towers.  It also features in many pantomimes.  Slapstick used to be very popular and is still used today to make people laugh.

An actual "slap stick" is a wooden paddle which was once used to make a smacking noise on stage.  While it's noisy, it doesn't hurt to be hit with a slapstick, so actors could hit each other with slapsticks during plays, fall down, and get a laugh from the audience.  It was one of the earliest known special effects.

The use of physical comedy in theatre goes back to ancient Greek times, almost three thousand years ago.  In the 16th century William Shakespeare used slapstick style scenes in some of his comedies. Later slapstick was used and popularised in British music hall theatre.

In the 1890's, an English comedian called Fred Karno came up with a type of comedy which didn't use words.  He is famous for the "custard pie in the face" joke used so often in slapstick.  He worked with other comedians, and his group became known as "Fred Karno's Army".  Members of this group included still well known comedians like Charlie Chaplin and Stan Laurel (of Laurel and Hardy).   Fred Karno is credited with inventing the style of slapstick still popular today.

When movies were first invented, they were silent.  Slapstick worked perfectly in silent movies as it was so visually funny, and many comedy movies were made.  Even when sound was introduced, slapstick movies still made people laugh.

You may have seen movies starring Charlie Chaplin, Buster Keaton, Laurel and Hardy, the Keystone Cops, the Marx Brothers or Abbott and Costello. 

More recently, great examples of slapstick are Monty Python, Mel Brooks movies and TV shows, and Mr Bean. 

Here's an interesting video to watch about the history of slapstick comedy.