Answer:
They were official arragements made by Yi Sŏng-Gye (who ruled as King Taejo) and his successors, which basically consisted in a land redistribuition throughout the various levels of officialdom, that created the new aristocracy of scholar-officials called the yangban.
Explanation:
Redden, Erica. An Unexplored Universe. Boston: Javelin Press, 2008.