PlonkSourceaPlonK is a PlonK-based proving system. As such, it provides a way to create succinct cryptographic proofs about a given predicate, which can be then verified with a low computational cost.
A polynomial protocol allows a prover to convince a verifier of the fact that certain algebraic identites between polynomials (polynomials that have been previously committed) hold when evaluated over a set of points. (In our implementation such set of points must be a subgroup of roots of unity.)