How would you define a sandbox MMO?

"Everyday we take the Massive daily posts and bring them to Dragoon discussions. We would like to thank Massively for their original content."

So yesterday on Twitter I conducted an extensive, exhaustive survey in which I asked, "Hai guyz, what makes a sandbox MMO a thing? You know?" It was probably a little less articulate than that. While I might be seen as the ultimate source of information in video games, the truth is that I'm struggling to come up with a precise definition of what, exactly, makes a "sandbox" MMO.

Interestingly enough, the responses that some friends sent back my way were as varied as could be, suggesting that this might be more of a murky area than I assumed. Considering how much we throw the term around, both on Massively and elsewhere, I think it might be beneficial to come to a consensus.

So how would you define a sandbox MMO? Is it the tools, the freedom, a lack of traditional leveling, the variety of non-combat activities, the tone, or something else entirely? Can you sum it up in one precise sentence?

TH