“Unbound” Variables
A symbol that has not been given a value by assignment or in a function call is said to be “unbound.”
ERROR Unbound variable NEWSYMBOL.
The use of “unbound” here is actually a misnomer, because NEWSYMBOL has a binding. The binding just doesn’t have any value. But old uses of terminology persist!
> (makunbound 'newsymbol); undo the assignment