What is "callback"

n. 1 The return of a situation to a previous position or state. 2 A return telephone or radio call; especially one made automatically to authenticate a logon to a computer network. 3 A product recall because of a defect or safety concern. 4 (context computing programming English) A function pointer passed to another function that the latter can call for notification purposes. 5 (context theater English) a follow-up audition (casting) 6 (context comedy English) a joke which references an earlier joke in the same routine

n. a request by the manufacturer of a defective product to return the product (as for replacement or repair) [syn: recall]

Callback can mean:

• Callback (comedy), a joke which refers to one previously told in a set of jokes including both
• Callback (computer programming), executable code that is passed as a parameter to other code
• Callback (telecommunications), the telecommunications event that occurs when the originator of a call is immediately called back in a second call as a response
• Callback verification, a method for e-mail address verification used in SMTP
• Web callback, a technology that provides telephone callback for websites

In computer programming, a callback is a piece of executable code that is passed as an argument to other code, which is expected to call back (execute) the argument at some convenient time. The invocation may be immediate as in a synchronous callback, or it might happen at a later time as in an asynchronous callback. In all cases, the intention is to specify a function or subroutine as an entity that is, depending on the language, more or less similar to a variable.

Programming languages support callbacks in different ways, often implementing them with subroutines, lambda expressions, blocks, or function pointers.

In telecommunications, a callback (also written as call-back) occurs when the originator of a call is immediately called back in a second call as a response.

A callback, in terms of comedy, is a joke which refers to one previously told in the set. The second joke is often presented in a different context than the one which was used in the initial joke. Callbacks are usually used at or near the end of a set, as the aim is to create the biggest laugh at the end of a comic set. The main principle behind the callback is to make the audience feel a sense of familiarity with the subject matter, as well as with the comedian. It helps to create audience rapport. When the second joke is told, it induces a feeling similar to that of being told a personal or in-joke.