What is a callback function?

Question

What is a callback function?

Answer 1

A callback function is a function you specify to an existing function/method, to be invoked when an action is completed, requires additional processing, etc.

In Javascript, or more specifically jQuery, for example, you can specify a callback argument to be called when an animation has finished.

In PHP, the preg_replace_callback() function allows you to provide a function that will be called when the regular expression is matched, passing the string(s) matched as arguments.