An honorific is a form of address used to people of high rank.
An honorific is something that is attached to the name but is not normally used elsewhere, e.g Mr, Sir, Mrs, Dr, Master. Contrast this with a title or position can appear without the person's name (e.g. the President, the Earl), and may be asssociated with a particular role or area (e.g. the US President, Financial Director, Earl of Cornwall).
Note also that medieval English kings were addressed as "Your Grace". "Your Majesty" is found in letters to King Henry VIII after about the time he broke with the Church of Rome (watch the gradual transition from "your grace" to "your highness" and "your majesty" in the letters addressed to Henry by his wives and daughters at http://englishhistory.net/tudor/letters.html). If you have examples of the use of "Your Majesty" before this time, please cite them here.
Honorifics in the SCA
|King or Queen||Your Majesty
My Liege (in some Kingdoms, only if you've sworn fealty)
Your Grace (if you're just rather old-fashioned)
|Crown Prince or Princess||Your Royal Highness|
|Prince or Princess||Your Highness|
|Duke or Duchess||Your Grace|
|Count or Countess||Your Excellency|
|Viscount or Viscountess||Your Excellency|
|Baron or Baroness||Your Excellency|
|Pelican or Laurel||Master or Mistress|
|Anybody else||My Lord/My Lady|