A Court is the organizational method by which a Queen holds power and consists of (at a minimum) a Queen and 12 Jeweled males who make up her First Circle. There are four named 'offices' within the male First Circle- Steward, Master of the Guard, First Escort, and Consort. (Courts may or may not contain a Consort and First Escort at the same time, their duties are similar and overlap in some ways.) In addition, a Queen may (but is not required to) have other Queens sworn to her as a female First Circle (who may additionally have Courts of their own), and additional members of her court serving in Second Circles, Third Circles, and so on. The higher the number of the circle one serves in, the less directly one serves that Court's Queen. (Source: Tangled Webs.) A great deal of Protocol deals with the forms and formalities of running a Court.
A ruling Queen of any area (from a village all the way up to a territory or realm) will have a court; however, a warlord ruling the same area (see Daemon Sadi, Prince of Dhemlan; Lucivar Yaslana, Prince of Ebon Rih; Saetan SaDiablo, ruler of Hell) does not form a court, and typically serves in the court of a Territory or other higher queen.
Caste & Court
Darker-jeweled males may serve in the courts of a lighter jeweled Queen. In the Realm of Terreille before it was purged by Jaenelle Angelline in Queen Of The Darkness, darker-jeweled males were frequently controlled with a Ring of Obedience. In Kaeleer, and in Terreille after the purge, Protocol is considered sufficient leash. In The Shadow Queen, Cassidy, a Rose-Jeweled Queen rules a Court which includes Warlord Princes who wear Opal and Green.