filename extension(n = noun.communication) extension, file name extension - a string of characters beginning with a period and followed by one or more letters; the optional second part of a PC computer filename; "most applications provide extensions for the files they create"; "most BASIC files use the filename extension .BAS"
is a kind of string
is a part of computer file name, computer filename, file name, filename
computer filename, extension, extension agent, extension cord, extension course, extension ladder, extension phone, extension service, file name extension, filename, telephone extension, university extension