A computer network is a group of computers connected to each other electronically. This statements can be refers as that the computers can "talk" to each other and that every computer in the network can send information to the others. Usually, this means that the speed of the connection is fast - faster than a normal connection to the Internet.
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As in the simple ways of explaining the word computer can also be refers to an object that can accept some input and produce some output. In fact, the human brain itself is a sophisticated computer, and scientists are learning more about how it works with each passing year. Our most common use of the word computer, though, is to describe an electronic device containing a microprocessor. A microprocessor is a small electronic device that can carry out complex calculations in the blink of an eye. You can find microprocessors in many devices you use each day, such as cars, refrigerators and etc.
For more information, you can refer to : http://www.howstuffworks.com/pc.htm