What the Hell is Community?

An inquiring mind wants to know what, in exacting detail, 'community' is supposed to be.

It seems to be a feel-good buzzword with no exact meaning whatsoever. It's a ritual word people say when they like what's going on.

But, you know, I could be wrong.

Specifically, want to be able to evaluate communities in reference to the ideal, to tell the difference between good and bad or healthy and less communities, and to differentiate communities from things that look similar but are different. (It looks like a duck, quacks like a duck, and tastes like broccoli.)