What is a packet?

In addition to the actual data, packets also contain header information.

The header of a packet contains both the originating and destination IP (Internet Protocol) address. The header also contains coding to handle transmission errors and keep packets flowing.

Header information can be compared to addressing an envelope. Like the header of a packet, an envelope contains the addresses of both the sender and the recipient, in order to keep track of who the envelope is from and who it is going to.