What is a packet?

In Summary:

A packet is a single unit of data that is sent across a network. Data, such as e-mail messages and web pages, are broken into packets before they are sent across the Internet. In addition to data, packets also contain header information such as the originating and destination IP (Internet Protocol) addresses and coding to handle transmission errors. Header information is used by routers to determine the path that packets will take to reach their destination.

Transmission Control Protocol/Internet Protocol (TCP/IP) makes use of packets to send information across the Internet. IP segments the data into packets, places header information into each packet and determines how much data can fit into a single packet. TCP sends the packets in sequence so that they arrive at their destination in the correct order. TCP also requests that any damaged packets be resent.