A security hacker is someone who explores methods for breaching defenses and exploiting weaknesses in a computer system or network. Hackers may be motivated by a multitude of reasons, such as profit, protest, information gathering, challenge, recreation, or evaluation of a system weaknesses to assist in formulating defenses against potential hackers.
Bruce Sterling, author of The Hacker Crackdown
A computer network is a set of computers sharing resources located on or provided by network nodes. Computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies based on physically wired, optical, and wireless radio-frequency methods that may be arranged in a variety of network topologies.
Network Packet
Fiber-optic cables are used to transmit light from one computer/network node to another.
Computers are very often connected to networks using wireless links.
An ATM network interface in the form of an accessory card. A lot of network interfaces are built-in.