In an interactive proof system, a prover (who knows the answer or solution) communicates with a verifier (who wants to confirm the correctness of the answer) through a series of messages. This interaction allows the verifier to gain confidence in the statement's correctness with high probability, even if they do not possess the entire output. The process typically involves multiple rounds of questioning and responding, where the prover answers specific challenges posed by the verifier. This has significant importance in cryptography and complexity theory, proving that certain problems can be more easily verified than solved.