File Extensions are a group of (2, 3 or 4) letters occurring after a period in a file name, indicating the format of the file. The File Extensions determines which Application can open and view that File.
A file extension or file name extension is the ending of a file that helps identify the type of file. For example, the file name “myfile.txt” has an extension of “.txt”, which designates a Text File.
A filename extension is an identifier specified as a suffix to the name of a computer file. The extension indicates a characteristic of the file contents or its intended use. A file extension is typically delimited from the filename with a full stop (period), but in some systems it is separated with spaces.