Nil

Definition: The value 'nil' is used to refer to something that has no value. This is different than 0 (a number with no value) or false (a boolean with a false value). The value 'nil' means "no value." That might be difficult to think about, many languages don't have an equivalent. C programmers have NULL, but that means "points to nothing," not exactly the same. Just know that 'nil' is used for things like undefined variables, or when a method doesn't return anything. When used in a boolean statement, it evaluates to 'false.'