An evaluator agent is an AI agent that reviews, scores, or validates the output of another agent before the result is accepted or finalized. It acts as a quality-control component and may also be called a critic in agentic workflows.
An agent that assesses another agent's results before those results are finalized. You can imagine one agent as manufacturing a product and a separate agent---the evaluator agent---testing that product before it is released. Critic is a synonym for evaluator agent.