Satire is the ridicule of vice or folly. Its ostensible goal is to take an individual person, a type of person, an individual folly, or a type of folly, and expose it to public scrutiny. Satire doesn't have to be funny, though it very often is.
The two most influential classical Latin satirists were Horace and Juvenal; Horace was the more gentle, general, and good-natured, while Juvenal had a sharper edge to his satires. Satires that follow these traditions are classified as Horatian or Juvenalian.
A third kind of satire is harder to define: it's known as Menippean or Varronian satire. Although Horatian
and Juvenalian satires are often formal verse satires, a well recognized genre, satire need not be in verse, and Menippean satire often
But it's also characterized by an almost formless form -- Menippean satires are conventionally chaotic in organization, and it's usually difficult (if not impossible) to pin down the specific targets of ridicule. Some good examples are Rabelais's Gargantua and Pantagruel and Laurence
Sterne's Tristram Shandy. The Russian theorist Mikhail Bakhtin devotes a lot of his attention to Menippean satire in general and Rabelais in particular, drawing attention to what he calls their dialogism--the competition of several voices within a literary work.
Satire is not the same thing as parody--the borrowing of the distinctive features of one work to make fun of them in another--although satire can use parody as a technique.
Menippean satire is a term employed broadly to refer to prose satires that are complex in nature, combining many different targets of ridicule into a fragmented satiric narrative. The form is named after the Greek cynic Menippus, and from suppositions about the nature of his lost works, which are more directly reflected in the Greek dialogues of Lucian and the works of Marcus Terentius Varro. Indeed, such satires are sometimes termed Varronian satire. Though Varro's own 150 books of Menippean satires survive only as quoted snippets, the genre was continued by Seneca the Younger. His Apocolocyntosis, or "Pumpkinification," is the only near-complete classical Menippean satire to survive. Menippus' tradition can be recognized in portions of Petronius' Satyricon, in the banquet scene "Cena Trimalchionis," where epic, tragedy, and philosophy are combined in verse and prose. It is also seen in Apuleius' Golden Ass, a combination of Menippean satire and comic novel.
The term has been used by classical grammarians and by philologists to refer to satires in prose; compare the verse satires of Juvenal and his imitators. Menippean satire moves rapidly between styles and points of view. Such satires deal less with human characters than with the single-minded mental attitudes, or "humours", that they represent: the pedant, the braggart, the bigot, the miser, the quack, the seducer. "The novelist sees evil and folly as social diseases, but the Menippean satirist sees them as diseases of the intellect," Northrop Frye observed, and instanced Squire Western in Tom Jones as a character rooted in the realism of the novel, but the tutors Thwackum and Square as figures of Menippean satire. Contemporary literary scholars such as Northrop Frye have attempted to classify Swift's A Tale of a Tub or Gulliver's Travels and Thomas Carlysle's Sartor Resartus as Menippean satires. Frye also instances Alice in Wonderland and its sequel, and Burton's discursive Anatomy of Melancholy.