tedster - 6:02 am on Nov 21, 2010 (gmt 0)
Classically, it means a site that a lot of other strong sites in the niche link to. Today, I think that's expanded to include REAL social media mentions. I'd also bet that navigational searches mean a whole lot.
But what is Google's "exact" formula today? I'm not in the loop on that, so I'm puzzling it out with everyone else.