Hi, first off, english is not my natural language, i'm german. But the term 'stack' is used here as well when it comes to amps. I'd like to enquire about when the threshold is crossed and you refer to an amp as a stack. My thoughts on this: If you look at the word, the term obviously comes from the verb 'to stack' and in the classical sense it was referring to a Marshall head with 2 4x12 cabs, a full stack, while a Marshall head with a single 4x12 was a halfstack. So is it as simple as that ? Two cabs on top of each other and a head on top of that is a stack ? I'd be inclined to say yes, but i don't feel like it is that easy. There are cabs that are meant to be driven without another cab like the ampeg fridge and i would refer to a 8x10 with a head as a stack as well. So if you follow down that line of argument, you could say that a head with a decent cab is a halfstack while a head with two decent cabs is a fullstack - decent means in this case that the head with a single cab would be enough to stand up against a drummer playing rock without breaking a sweat. A cab that houses enough speakers to compete with such a full stack is referred to as full stack as well in this case. But what about the small cabs that came into fashion in the recent past, such as 2x10 cabs, or even the popular 1x12 cabs? With 2 stacked 1x12 or 2x10 cabs and a head on top, you have three boxes stacked on top of each other, but you only get what a halfstack (i.e. a head with a 4x10 cab or a 2x12 cab) delivers. So is a 2x 2x10 plus head a stack as well as a single 8x10 plus head ?