Octavian Country Day School is the elite, all-girls day school that the pretty committee attends. It is located in Westchester, New York, and offers just about everything; a starbucks booth, phenomenal sports teams, and gorgeous facilities. It's brother school is Briarwood Academy. OCD also stands for Obsessive Compulsive Disorder, which means that the author is actually making fun of the people in the school because The Clique is obsessed with fashion, in a sense.
In Bratfest at Tiffany's, the Briarwood boys have to come to OCD because the Briarwood Academy is flooded, and Massie fears that she will become an LBR because the boys will take over. The name of the school then turns into Briarwood-Octavian Country Day School.