Four philosophical schools. Vaibhashika, Sautrantika, Chittamatra, and Madhyamika
Four Philosophical Systems, the four schools of philosophy, four systems of tenets. Those of the Vaibhashikas {bye brag tu smra ba} Sautrantikas {mdo sde pa} Vijnanavadins {rnam shes su smra ba} or {sems tsam pa} and Madhyamikas {dbu ma pa}