Sir is an honorific used as a title (see Knight), or as a courtesy title to address a man without using his given or family name in most English speaking cultures. It is often used in formal correspondence (Dear Sir, Right Reverend Sir). The term was once reserved for use only towards equals, one of superior rank or status, such as an educator or commanding officer, an elder (especially by a minor), or as a form of address from a merchant to a customer. Equivalent terms of address are "ma'am"… (More on Sir)