A packet is, in a sense, a piece of data that has been encapsulated inside other data. This other data can be anything, but in networks, usually comprises of the source of the packet, its destination and a checksum.

The benefit of using packets is that they are discrete objects. Information can be split up into numerous packets which are sent out over a network. Each packet contains the information necessary to get it to its destination. The receiving end can reassemble the packets, and request that any lost packets be sent again. This is the basis behind TCP/IP and other wide area networks.