hobby tribe
n.— «The most fanatical of user groups can be thought of as “hobby tribes,” a phrase coined by science fiction writer David Brin. Hobby tribes are very informed, very connected, very smart customers. They band their enthusiasms together and become the experts. In some smaller niches they become the market too.» —“Book Review: In Praise of Expert Amateurs & Passionate Hobbyists” by Nicole-Anne Boyer Fuzzy Signals Jan. 6, 2005. (source: Double-Tongued Dictionary)