Pipiltin

The Pipiltin (sg. "pilli") were the noble social class in the Mexica Empire. They are below the ruling nobles in the civilization's social structure and above the commoners who achieved noble status due to an outstanding deed in war. These people were members of the hereditary nobility and occupied positions in the government as ambassadors and ministers, the army and the priesthood. The subclasses within the "Pipiltin" were: tlahtohcapilli (a tlahtoani's son), tecpilli or teucpilli (a teuctli's son), tlazohpilli (son of legitimate wife), and calpanpilli (son of a concubine).
Children of the "Pipiltin" were given extensive education in preparation for the role they will play in their adult life. They were sent to the "calmecac", which was the center for higher learning, to study the ancient wisdom as well as "elegant forms of speech, ancient hymns, poems and historical accounts, religious doctrines, the calendar, astronomy, astrology, legal precepts and the art of the government."
Origin.
As the Aztecs began settling what would later become their homelands, an elite emerged (the "Pipiltin") that claimed descent from the Toltecs, the former empire of Central Mexico. The new hereditary elite unified the clans that had been the center of Aztec life and paved the way for a conquest empire. Some sources describe the "Pipiltin" as the offspring of "tlahtohqueh" and "teteuctin", which were different social classes within the ruling nobility. 
The name was also where the Pipil people of western El Salvador get their name, as they are descendants of Toltec people who migrated and settle in El Salvador.
The authority and prestige of the "Pipiltin" were based on the belief that they descended from the original migrant founders of the Aztecs and came from a mythical place. Due to this heritage, they enjoyed privileges such as special family dispensation, the use of privilege goods and dwellings that were appropriate to their station.