From LQWiki

A packet is a small chunk of data to be sent over a network in one go. Larger amounts of data can be split up into several packets and transmitted individually. One usually prefixes it with the protocol directly used to transmit it, such as an IP packet or a UDP packet (also called a datagram).

Packets might not arrive for various reasons, such as unplugged network cables or corruptions (see packet loss). In these cases, a transmissions protocol like TCP/IP is employed to automated the querying and resending of lost packets.

Firewalls can use packet filters to stop unwanted traffic.

See also

• Traceroute