(2) To specify the properties, particularly visible properties, of an object. For example, word processing applications allow you to format text, which involves specifying the font, alignment, margins, and other properties.
(n.) A specific pre-established arrangement or organization of data. Data in a file is stored in a format that is established by whatever application created the file (i.e., organized the data) and typically needs to be read by the same or similar program that can interpret the format and present the data to the user on the computer screen.
Almost everything associated with computers has a format.