A variable which has no value is said to be void, attempting to reference the value of such a symbol will result in an error. It is possible for the most recent binding of a variable to be void even though the inactive bindings may have values.
Returns true if symbol is bound to a variable.
This function makes the current binding of symbol as a variable be void, then returns symbol.
(setq foo 42) ⇒ 42 foo ⇒ 42 (boundp 'foo) ⇒ t (makunbound 'foo) ⇒ foo (boundp 'foo) ⇒ () foo error→ Value as variable is void: foo