**Definition.**- An ALGORITHM is a well-defined computational procedure that transforms inputs into outputs, achieving the desired input-output relationship.
**Definition.**- A computational PROBLEM is a specification of the desired input-output relationship.
**Definition.**- An INSTANCE of a problem is all the inputs needed to compute a solution to the problem.
**Definition.**- A CORRECT algorithm halts with the correct output for every input instance. We can then say the algorithm SOLVES the problem.