What do you call a ceremony when someone becomes lord or lady?

When Her Majesty the Queen the knights someone (like Sir Paul McCartney, for example), it takes place at an Honours ceremony. If someone is made a lord or lady (often in recognition for their services to politics, or business, for example) they are "ennobled" (literally "made noble") or "elevated to the peerage", the peerage being all the aristocracy (dukes, earls, baronets). People like Baroness Thatcher are "life peers", i.e. when they die the title will not pass down to their children or to anyone else in the family. Members of the aristocracy, who pass their titles on from generation to generation, are "hereditary peers".