Its a credit given to companies backed by an accelerator.

Even ones that can't think of anything to do with it? I wish I had these problems :-/

It's given out like candy, if not the 100k one you can surely get several thousands worth of credits for server hosting, either on Azure or through Amazon.

Can confirm - with my MSDN license I get a $150/mo credit for any development/test instances. As long as I have a valid license (and they offer the deal) I'll get the credit.

which one?

I know Startupbootcamp has these deals for their batches. A similar deal is available for Google business users.