A programming language formerly much in vogue among users of microcomputers. Forth operands are held on a stack, and programs take the form of strings in reverse Polish notation. A vital feature of Forth is that a symbol (a WORD) can be associated with any program string, and such a user-defined word can then be used in expressions on equal terms with the system words (operators). Forth is now little used, but the same principles are found in PostScript.