In feudalism, a lord (French: seigneur) is an aristocrat who claims dominion over a portion of land and the produce and labour of the serfs living thereon. They are normally hereditary and owed similar allegiance to the monarch. Generally, the word lord is applied to superiors of many kinds, e.g. landlord, and in many countries in Europe is used as a general title of address equivalent to the English "Mr": e.g. Signore, Herr.
The etymology of the English word "lord" goes back to Old English hlaf-weard (loaf-guardian) -- reflecting the Dark Age duty of a superior to provide food for his followers. The female equivalent is Lady, which might come from words meaning loaf-kneader.
In the United Kingdom, the hereditary lords were until recent years automatically members of the House of Lords, the upper house of Parliament. There are five ranks of peer, namely Duke, Marquess, Earl, Viscount, and Baron. The title is also applied by courtesy to certain of their children, e.g. the younger sons of dukes and marquesses are known as "Lord (firstname) (lastname)".
The title is used by senior judges: the Law Lords or "Lords of Appeal in Ordinary" who are life barons, judges of the Court of Appeal of England and Wales, who are known as "Lords Justices of Appeal" and judges of the Scottish Court of Session who are known as "Lords of Council and Session";
Another English title is lord of the manor, which is not a peerage and does not carry parliamentary rights. The title merely indicates the owner of a manor who has certain local rights, and is not used socially.