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 languages such as Lisp or Forth have their own idiosyncratic syntax.(2001-05-14)