What is the name of system which ranked society in following order King Knights Merchants Serfs?

The system that ranked society in the order of King, Knights, Merchants, and Serfs was called the feudal system. Feudalism was a political system that was based on land ownership and a strict social hierarchy. The king was the highest-ranking person in the feudal system and owned all the land in the kingdom. He would grant land to knights, who would in turn swear loyalty to the king and provide military service. The knights would then grant land to merchants and serfs, who would work the land in exchange for protection.