affinity group 
noun chiefly US
A group of people linked by a common interest or purpose: feminist and lesbian affinity groups...
- In the session we learned at least two important lessons: the need to establish and maintain links with other members of an affinity group and the usefulness of vinegar in dealing with the effects of tear gas.
- An affinity group of older women from Montreal, were the first to approach the fence.
- I quickly began searching for my affinity group.