A network is simply two or more computer systems connected together to allow them to communicate and share information.
Networks allow us to:
Send and receive emails (communication)
Share peripherals like printers
Work simultaneously on tasks and share files
Have a roaming profile, meaning you can use almost any machine on the network
There are some disadvantages, such as:
Hardware, including servers like File and Web servers are expensive
Specialist staff (like a Network Manager) may be required to look after the network
If any of the hardware fails, the network may not function properly
A greater risk from viruses
Any machine which is not part of a network is known as a Stand Alone Machine. This may mean that it doesn't have a Network Interface Card (NIC), but often means that the machine is simply not required to be connected to a network.