Filename extension

A filename extension is a suffix (separated from the base filename by a dot or space) to the name of a computer file applied to indicate the encoding of its contents or usage. Examples of filename extensions are,,, and . Some file systems limit the length of the extension (such as the FAT file system from PC-DOS/MS-DOS not allowing more than three characters and IBM’s VM/CMS not allowing more than 8) while others do not. Unix filesystems accept the separator dot as a legal character.