Alternatively called a short file name, the 8.3 format is a file format that supported a maximum file name of eight characters and up to a three character extension. For example, in the image you can see the file name is Regedit and the extension is .exe.
Early versions of MS-DOS and Windows only supported 8.3 format files. However, today all versions of Windows and other modern operating systems support long file names.
In the Windows command line, you can see each files short name using the dir /x command.