Other forms: peerages
The system of giving people titles like "Lord So-and-So," or "The Duchess of Wherever" is called peerage. The title itself is also referred to as a peerage.
In a monarchy like the United Kingdom or Saudi Arabia, a peerage is a legal classification of all the ranks bestowed on the nobility. So if a country has lords, ladies, dukes, duchesses, earls, and countesses, it's the peerage that keeps track of the titles and who holds them. If you're bestowed such a title, you receive a peerage: "My grandmother inherited a peerage when her uncle died, and that's when my family got that castle in Scotland."