The social groups to which we become affiliated because they validate us in some fashion. Usually these microtribes are insular, or nearly so, and brook few easy intrusions, nor espouse views that conflict with their worldview, rock the boat, or fail to comply.

Alas, I cannot take credit for the existence of this word, but I can take credit for defining it in the fashion that I have. He was the first person I witnessed use this term.