gRPC is a high-performance, low-latency messaging protocol developed by Google that enables fully duplex and bidirectional messaging between clients and servers. It sends binary data over HTTP/2 and is often used for data communication due to its lightweight and efficient performance. gRPC-Web, on the other hand, is a distinct protocol that exists solely in a browser and acts as a translation layer between gRPC and applications, allowing for easier coordination between browsers and backend services while providing compatibility and removing the need for separate HTTP clients.