A nORmal (deterministic) Turing Machine that has a "guessing head" - a write-only head that writes a guess at a solution on the tape first, based on some arbitrary internal algORithm. The regular Turing Machine then runs and returns "yes" OR "no" to indicate whether the solution is cORrect. A nondeterministic Turing Machine can solve nondeterministic polynomial time computational {decision problems} in a number of steps that is a {polynomial} function of the size of the input (1995-04-27)