About file formats
Files are self-contained objects on a computer that store information. Several different file types serve a variety of purposes. Some store information about the operating system and user settings, while others contain programs, written documents, graphics, or sound.
A particular file format is often indicated as part of a file's name by a file name extension (suffix). Conventionally, the extension is separated by a period from the name and contains three or four letters that identify the format.