The Lord is God in the Old Testament, who includes Jesus Christ beginning with Christianity. The word "Lord" is used to translate the tetragrammaton and is by far the most-referenced word in the Bible.
In feudalism, a lord, or noble, was the person to whom the king granted large tracts of land. He in turn rented parcels of this land to vassals. A serf would swear the oath of fealty to the lord, or "keeper of the loaves" (Old English hlaf-weard (loaf-ward).