PH (complexity)

In computational complexity theory, the class PH (short for "Polynomial Hierarchy") is a way of categorizing decision problems based on their complexity relative to polynomial-time computations. It is a hierarchy of complexity classes that generalizes the class NP (nondeterministic polynomial time) and co-NP (problems whose complements are in NP). The polynomial hierarchy is defined using alternating quantifiers and is composed of multiple levels, where each level corresponds to a certain type of decision problem.