The purpose of a network protocol in communication systems is to establish rules and conventions for data exchange between hardware and software devices. Protocols ensure that devices can communicate effectively, regardless of their underlying technology or architecture. They help govern various aspects of communication, including data format, error handling, and synchronization. Examples of network protocols include TCP/IP, which governs internet communication, and HTTP, which is used for transferring web pages. Properly defined protocols are essential for seamless and reliable communication.