A protocol artist, in my very narrow definition, is one that builds the creative endeavor on the design of a protocol, the design of a system. But then once the protocol has been created, that system can be instantiated by not just me.
Primavera De Filippi, Strange Rules: Protocol Art at the Venice Biennale
Protocol art is a little more opinionated than that; our systems/protocols are set up to enact a certain kind of interaction and outcome—a little more like an AI agent than an arbitrary feedback system.
Mat Dryhurst, Mat Dryhurst on Becoming Infinite