Every file name has a dot (.) after it and some letters after the dot. File extension is the suffix after the filename, that is, the letters that come after the ‘dot’. It tells the user the nature of the file and the kind of applications that can open it. For instance, in the file name justin.mp3, the file extension is “mp3”, which indicates that it is a media file and media applications like Windows Media Player, VLC, etc. can open it.