FreeVariable - benchristel/benchristel.github.io GitHub Wiki

The free variables (or, more precisely, the free Identifiers) of a Routine are those that are referenced within the Routine but not declared as locals or Parameters. In most programming languages, the definitions of free Identifers are looked up in the Routine's enclosing LexicalScope.

See: https://en.wikipedia.org/wiki/Free_variables_and_bound_variables