A joke is a display of humour in which words are used within a specific and well-defined narrative structure to make people laugh and is not meant to be taken seriously. It takes the form of a story, usually with dialogue, and ends in a punch line. It is in the punch line that the audience becomes aware that the story contains a second, conflicting meaning. This can be done using a pun or other word play such as irony or sarcasm, a logical incompatibility, nonsense, or other means. Linguist Robert Hetzron offers the definition:

A joke is a short humorous piece of oral literature in which the funniness culminates in the final sentence, called the punchline… In fact, the main condition is that the tension should reach its highest level at the very end. No continuation relieving the tension should be added. As for its being "oral," it is true that jokes may appear printed, but when further transferred, there is no obligation to reproduce the text verbatim, as in the case of poetry.

It is generally held that jokes benefit from brevity, containing no more detail than is needed to set the scene for the punchline at the end. In the case of riddle jokes or one-liners the setting is implicitly understood, leaving only the dialogue and punchline to be verbalised. However, subverting these and other common guidelines can also be a source of humor—the shaggy dog story is in a class of its own as an anti-joke; although presenting as a joke, it contains a long drawn-out narrative of time, place and character, rambles through many pointless inclusions and finally fails to deliver a punchline. Jokes are a form of humour, but not all humour is a joke. Some humorous forms which are not verbal jokes are: involuntary humour, situational humour, practical jokes, slapstick and anecdotes.

Identified as one of the simple forms of oral literature by the Dutch linguist André Jolles, jokes are passed along anonymously. They are told in both private and public settings; a single person tells a joke to his friend in the natural flow of conversation, or a set of jokes is told to a group as part of scripted entertainment. Jokes are also passed along in written form or, more recently, through the internet.

Stand-up comics, comedians and slapstick work with comic timing, precision and rhythm in their performance, relying as much on actions as on the verbal punchline to evoke laughter. This distinction has been formulated in the popular saying "A comic says funny things; a comedian says things funny".