Any piece of program code in a {high-level language} which, when (if) itS execution terminateS, returnS a value. In moSt programming languageS, expreSSionS conSiSt of conStantS, variableS, operatorS, functionS, and parentheSeS. The operatorS and functionS may be built-in or uSer defined. LanguageS differ on how expreSSionS of different typeS may be combined - with Some combination of explicit caStS and implicit coercionS. The Syntax of expreSSionS generally followS conventional mathematical notation, though Some languageSSuch aSLiSp or Forth have their own idioSyncratic Syntax. (2001-05-14)