Manumission
Manumission is the act of freeing a slave, done at the will of the owner.The term is Middle English and is derived from the Latin manumittere. The act of manumission dates back to ancient Rome. Popes, emperors, and minor landholders all are counted among those who practised it. In the middle ages serfs were freed through a form of manumission.
The process differed from time to time and lord to lord. High productivity, loyal service, or even buying your way out of service were all ways slaves or serfs were freed under manumission.
Manumission was a tenuous process at best. In ancient Rome, freed slaves were not "freeborn" and were still required to grovel in the presense of their former masters. In the middle ages, for serfs who had obtained their freedom and farmland, they often would give up their land in exchange for the protection of their former feudal masters in times of trouble. In times of bad harvest, the serf could find themselves once again attached to the land of a noble for lack of any other means of survival.
For these reasons, manumission is not the same as the Emancipation when all slaves in Rebel States were set free during the American Civil War.