The answer is: "a system in which the Spanish monarchs granted the conquistadors the right to demand labor from Native Americans"
Spanish conquistators were given land in the Americas. Those lands were vast and included any communities or cities in that land. The natives in these comunities had to provide tributes, as well as work a certain amount of time on the plantations or mines. In exchange, the land owner was responsible for their well-being and for educating them on Christianity.