Sir is an honorific address used in a number of situations in many anglophone cultures. The term can be used as a formal prefix, especially in the Commonwealth, for males who have been given certain honors or titles (such as knights and baronets), where usage is strictly governed by law and custom.
The term is commonly used as a respectful way to address a man, usually of superior social status or military rank. Equivalent terms of address to females are "ma'am" or "madam" in most cases, or in the case of a very young woman, girl, or unmarried woman who prefers to be addressed as such, "miss". The equivalent term for a knighted woman or baronetess is Dame, or "Lady" for the wife of a knight or baronet