Mac is the Gaelic for "son" and is a very common element in Scottish and Irish surnames. It is often believed in the U.S. that Mac is Scottish and Mc is Irish, but this is not true. Mc is actually an abbreviation of Mac, and at one time was also written M'.

Philip D. Smith, tartan scholar and historian, says that in an early book on Highland music the author spelled his own family name three different ways on the first two pages: MacDonald, McDonald, and M'Donald.