The format of something is the way or order in which it is arranged and presented.

The format of a piece of computer software or a musical recording is the type of equipment on which it is designed to be used or played. For example, possible formats for a musical recording are CD and cassette.

To format a computer disk means to run a program so that the disk can be written on.

To format a piece of computer text or graphics means to arrange the way in which it appears when it is printed or is displayed on a screen.