In slang terms, a coterie is what we more crudely refer to as a “click”: a close (often select or fashionable) crowd of people having with a mutual objective or interest. In a junior high context, that mutual interest is to be popular. In a country club context, that mutual interest is to be envied. Wait – are those basically the same thing?
Example: Jan hated it, but it was a fact of life. In every A&D firm she had ever worked for that had over 50 employees, impenetrable coteries of young architects and designers existed, making her feel like an outsider the moment she was assigned a desk.