Satire is a genre that sets out to improve bad behavior through sarcasm and irony. A satirist humorously depicts a current state of affairs, and hopes that by doing so, he might improve it. It's all about making fun of vices, foolishness, and shortcomings, so that the subject can improve. Satire can be found in novels, plays, short stories, and well, almost anywhere, even The Simpsons.
Satire started way back in the classical period. Horatian satire, for example, is derived from the ancient poet Horace and is known for using gentle, self-deprecating humor to make fun of general foolishness. Then there's Juvenalian satire, named after the Roman Juvenal, which is a lot harsher, and a lot less funny. Well it's still funny, but you might cringe while chuckling.
In English literature, satire experienced a bit of a revival during the 18th century, when folks like Alexander Pope and, even more famously, Jonathan Swift, poked fun of society for all kinds of weaknesses. One of the most famous satires of all time is Jonathan Swift's A Modest Proposal, which suggests that Irish folks raise themselves out of poverty by selling their children as food for rich folks. He was kidding. We hope. (That, by the way, is an example of Juvenalian satire.)
Satire is still in our midst. What can we say, the people love it. If you're in the mood for some modern-day fun-having, check out The Onion, The Colbert Report, 30 Rock, Clueless, and yes, The Simpsons.