A close group, a network of friends who from the beginning are never part of any other group. They only talk to those inside the clic, hangout with the clic, etc.
Yes, there can be leaders among the clics, which then the rest of the group are called followers.
This term is probably better use in middle school, as high schoolers tend to grow away from clics, and actually talk to other people and be a real person.
Classic movie :Mean girls
The popular clic
"Those with gifted intelligence and slightly akward social skills" aka nerds
The regular clic