A computer network is a group of inter-connected computers, the first network was the (ARPA).
computer networks could be Wired :

1. Twisted-Pair Wire
2. Coaxial Cable
3. Fiber Optics

or Wireless:

1. Terrestrial Microwave
2. Communications Satellites
3. Cellular and PCS Systems
4. Wireless LANs
5. Bluetooth

Computer networks could be classified according its scale:

• LAN local area networks
• WAN wide area networks
• MAN Metropolitan Area Networks
• PAN personal area networks

also, topologically:

1. star
2. ring
3. bus
4. mesh
5. tree

networking components such as:

• hub
• switch
• router
• repeater
• access points
• bridges
• NIC network interface card