No it's not mining. Your contribution is not monetary. Your contribution is that your computing power gets used to crunch on a small part of an extremely large problem.
The idea is instead of building a super computer for bajillions of bucks that the problem is split down into millions of manageable chunks that anyone can contribute some computing power toward. So instead of the super computer doing the job, it's millions of PC users around the world.
This is the one I used to do
foldingathome.org
But it seems World Community Grid is so much more.
With F@H you would download a job, your system would work at it for a while (usually your GPU, and I mean like 99% utilisation or however much you are willing to surrender), then once it done it uploads the job back and fetches itself another to work on. Could be stopped at any time and resumed at will.