What is Lord?

Legal Definition
Lord is an appellation for a person or deity who has authority, control, or power over others acting like a master, a chief, or a ruler. The appellation can also denote certain persons who hold a title of the peerage in the United Kingdom, or are entitled to courtesy titles. The collective "Lords" can refer to a group or body of peers.
-- Wikipedia
Legal Definition
In English law. A title of honor or nobllity belonging properly to the degree of baron, but applied also to the whole peerage, as in the expression "the house of lords." 1 Bl. Comm. 396-400. A title of office, as lord mayor, lord commissioner, etc. In feudal law. A feudal superior or proprietor ; one of whom a fee or estate is held.
See also
-- Black's Law Dictionary
Legal Definition
In England, this is a title of honor. Fortunately in the U. S. no such titles are allowed.
-- Bouviers Law Dictionary
Legal Definition
A landlord; a feudal proprietor; a peer; an official title.
-- Ballentine's Law Dictionary