It seems that everyone and their granny is trying to create some sort of stack offering these days. Look at all the brouhaha – HP buying 3Par, Dell buying Compellent, all kinds of partnerships being formed left and right. Stacks are hot.
To the uninitiated, a stack is what you can get when a vendor is able to offer multiple products under a single umbrella. For instance, being able to get servers, an OS, a DB, an email system, storage and network switches from a single manufacturer (not a VAR) is an example of a single-sourced stack.