Happy Birthday Ma'am
Why I wonder is the Queen addressed as Ma'am?
Surprisingly this is not as easy to find out as one would think. The closest explanation I have come upon (although more of a statement of fact than an explanation) is that like so many other British unexplainable quirks it comes from tradition. Ma'am is simply the abbreviated version of Madam.
Should you come face to face with the Queen on her birthday this weekend or on another occasion do take note that the correct protocol is to address her as Her Majesty when first introduced and then Ma'am thereafter.
The Queen's birthday is tomorrow, 21st April, but the official celebration takes place on 17th June 2017 and is celebrated with the Trooping of the Colour.
Happy Birthday Ma'am!