A protocol is a set of formal rules and conventions that define how data is transmitted and communicated between devices or systems within a network. Protocols ensure that information is exchanged accurately, securely, and efficiently by specifying the format, timing, sequencing, and error handling of messages. Common examples include HTTP for web communication, TCP/IP for internet connectivity, and SMTP for email transmission. By following established protocols, different hardware and software can interact seamlessly, regardless of their underlying architecture.