A packet is a small segment of data that is transmitted over a network. It is a fundamental unit of communication in network systems, allowing data to be efficiently sent and received between devices. When data is transmitted over a network, it is broken down into smaller, manageable pieces called packets. Each packet contains not only a portion of the data but also essential information such as the source and destination addresses, error-checking codes, and sequencing details to ensure that the data can be accurately reassembled at the receiving end. This method of data transmission is used in various networking protocols, including the Internet Protocol (IP), to facilitate reliable and efficient communication across diverse and complex networks.