Humor

Humor is difficult to define. Everyone finds differing things funny; no two people can agree on what makes something funny.

There are many kinds of humor. There are jokes, which can be further broken down by kind of joke (knock-knock, one-liner, etc.); physical humor (slapstick, spit-takes); puns, limericks, and Spoonerisms; irony; and others.

Jokes

A joke can be elaborate or simple. The simplest jokes consist of the "setup", usually a question, followed by the answer or "punchline". The punchline may be a pun, or it may not bear too much relation to the setup. A perfect example of this is the following joke:

Q: Why did the chicken cross the road? A: To get to the other side!

This most likely does not strike you as funny (five-year-olds seem to respond best to this one), because the punchline does not seem to have too much to do with the setup. Consider, however, the progression of this joke:

Q: Why did the hippopotamus cross the road?
A: Because it was glued to the chicken!

You can continue in this vein until you're sick of the whole thing or your audience needs a nap, whichever comes first.

Also in the simple-joke category are knock-knock jokes. These usually consist of five lines and involve a Pun. An oldie but goodie goes like this:

Person 1: Knock-knock.
Person 2: Who's there?
1: Annapolis.
2: Annapolis who?
1: Annapolis a fruit!