I believe # of reads, likely within a certain period of time (month, 3 months ??).
Yes. But does anyone actually KNOW? For instance, I have maybe 4 blog posts in the last week or two that would culminate to half a thousand reads. Or do you need one blog with a lot for a perminant status? or is it temporary? I'd just like details is all 
A simple query I impose; how exactly are certain individuals' blogs put at the status of a "top blog"?