A piece of a message transmitted over a packet-switching network. One of the key features of a packet is that it contains the destination address in addition to the data. In IP networks, packets are often called datagrams.
A packet switched network is where individual packets each follow their own paths through the network from one endpoint to another.
Password Authentication Protocol is a simple, weak authentication mechanism where a user enters the password and it is then sent across the network, usually in the clear.
Password cracking is the process of attempting to guess passwords, given the password file information.
Passive wiretapping, usually on a local area network, to gain knowledge of passwords.
A patch is a small update released by a software manufacturer to fix bugs in existing programs.
Patching is the process of updating software to a different version.
Payload is the actual application data a packet contains.