Packet Switching

The networks that had been designed to support voice-conversations provided a dedicated, switched path to the caller and the callee for the duration of the call, and then released all of the segments for use by other callers. Data networks were designed to apply a very different principle. Messages were divided into relatively small blocks of data, commonly referred to as packets. Packets despatched by many senders were then interleaved, enabling efficient use of a single infrastructure by many people at the same time. This is referred to as a packet-switched network, in comparison with the telephony PSTN, which is a circuit-switched network. The functioning of a packet-switched network can be explained using the metaphor of a postal system (Clarke 1998).
http://www.anu.edu.au/people/Roger.Clarke/II/OzI04.html