This strangely named predicate is Prolog's equivalent to the not (often written as which stands for negation) of predicate logic. It is not named not/1 because we it turns out that we cannot easily implement classical negation in Prolog.
\+/1 takes a Prolog goal as its argument.
?-will succeed if man(jim) fails and will fail if man(jim) succeeds.
\+( man(jim) ).