Protocol design refers to the process of creating rules and conventions for communication between devices or systems in a network. It ensures that data is transmitted accurately and efficiently, allowing different devices to understand each other. This is crucial for the functionality of the internet and various applications. In computer networking, protocols define how data is formatted, transmitted, and received. Examples include HTTP for web browsing and TCP/IP for internet communication. Effective protocol design considers factors like speed, reliability, and security to meet the needs of users and applications.