A callback function is a function that is passed to another function as parameter. Callback function is called inside other Function. A callback function is essentially a pattern. Use of a callback function is also known as a callback pattern.
About Callback here the hide method accepting 2 parameters. First parameter is for hiding speed & the second parameter is our Callback function. Which contains a simple alert message. This message will call only after the paragraph is hide. This is a simple example.