intelligent plea

a defendant's plea of guilty based on reasonably competent advice is an intelligent plea not open to attack on the ground that counsel may have misjudged the admissibility of the defendant's confession; whether a plea of guilty is unintelligent and therefore vulnerable when motivated by a confession erroneously thought admissible in evidence depends as an initial matter, not on whether a court would retrospectively consider counsel's advice to be right or wrong, but on whether that advice was within the range of competence demanded of attorneys in criminal cases

Defined by the Supreme Court in - McMann v. Richardson, 397 U.S. 759 (1970).