A packet is a unit of data that is routed between an origin and a destination on the Internet or any other packet-switched network. When any file (such as e-mail message, HTML file, Graphics Interchange Format file, Uniform Resource Locator request) is sent from one place to another, the Transmission Control Protocol (TCP) layer of TCP/IP divides the file into smaller chunks ideal for routing.
Packet is a Network model or layering concept used to explain how communication functions are organized, encapsulated, and passed between systems.
This concept helps teams separate physical media, addressing, transport, and application behavior so troubleshooting and design discussions stay precise.
Additional Resource: IETF Internet Architecture Board Network Guidance.