hadoop is platform for performing distributed computing...

Hadoop is currently aimed at “big data” problems (say, processing Census Bureau data). The nice thing about it is that a Hadoop cluster scales out easily, and there are a number of providers who will let you add and remove instances from a Hadoop cluster as your needs change to save you money. It is the kind of system that lends itself perfectly to cloud computing, although you could definitely have a Hadoop cluster in-house.

While the focus is on number crunching, I think that Hadoop can easily be used in any situation where a massively parallelized architecture is needed.