A "protocol" in networking is a set of rules and conventions that govern how data is transmitted and received over a network. It dictates the format, timing, and sequence of messages exchanged between devices, ensuring successful communication. Protocols can vary based on their function, such as TCP/IP for internet communications, HTTP for web data transfers, and SMTP for email. The adherence to agreed-upon protocols enables interoperability between various systems and devices, facilitating consistent data flow and efficient network performance.