Distributed Computing simply means taking a huge problem and splitting it up into chunks, these chunks are then sent over a 'Net to a computer where they are processed, either manually or by a computer program. You can do many things with distributed computing, some of them criminal(Distributed Denial of Service Attacks, for instance).
Distributed doesn't necessarily mean "sent over a Net to a computer." For example, multi-core microprocessors can do distributed computing using shared memory for communications.
Distributed Computing can be used to study or discover things. It can be used to study molecules and their reactions, it can be used to study mathematical concepts, simulate physical forces, study genetics and protein folding, and many other things. A good website to discover Distributed Computing projects is www.aspenleaf.com 
See Also: Category Concurrency
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