Slapstick is a very old form of comedy, dating as far back as the Renaissance in Europe. There are also people familiar with the genre that argue that it has been present since the Middle Ages.
A very simple example of slapstick is a form of physical comedy in which the actor or actors use physical motions to amuse the audience. They can be as simple as walking into a wall and falling down or more complex and include several parts or processes.
An example of slapstick, among thousands in their repertoire, would be that of the three stooges. Larry talks to Curly as they walk across the stage, they stop to talk and stand, then Curly turns quickly to walk away and walks right into a pole and falls on his backside.