A network protocol is a set of rules and standards that define how data is transmitted and received across a network. These protocols facilitate communication between devices, ensuring that data packets are sent, received, and interpreted correctly. Key protocols include Transmission Control Protocol (TCP), which ensures reliable data transfer, and Internet Protocol (IP), which addresses the data's routing. Protocols can also govern aspects like error checking, data compression, and security measures, making them essential for both network performance and overall functionality of various internet services and applications.