1) Functional programming is a style of programming that emphasizes the evaluation of expressions rather than the execution of commands. Erlang programming language is described as a functional programming language. Erlang avoids the use of global variables that can be used in common by multiple functions since changing such a variable in part of a program may have unexpected effects in another part.
2) In an earlier definition from the ITU-TS, functional programming is "a method for structuring programs mainly as sequences of possibly nested function procedure calls." A function procedure is a relatively simple program that is called by other programs and derives and returns a value to the program that called it.