What is the Grid?

The short answer is that, whereas the Web is a service for sharing information over the Internet, the Grid is a service for sharing computer power and data storage capacity over the Internet. The Grid goes well beyond simple communication between computers, and aims ultimately to turn the global network of computers into one vast computational resource.

That is the vision. But the reality is that today, the Grid is a "work in  progress", with the underlying technology still in a prototype phase, and being developed by hundreds of researchers and software engineers around  the world.

Take a look at the Grid Cafe - "The place for everybody to learn about the Grid"