The word encomienda means "(those) entrusted" and was a labor system used for Spanish colonies, mainly in the New World. It meant that tribute and labor was expected of the indigenous native tribes by Spaniards who controlled their lands (which was still considered owned by the natives). In return, the natives were granted military protection, education, and teachings of the Christian faith. It was meant to benefit both Spaniard and native but it seems as though the Spaniards always got the upper hand.
The encomiendas followed the earlier Spanish practice of requiring service from Muslims and peasants following the Reconquista (reconquest of Spain from the Moors). In practice, they became little more than involuntary servitude.