Since modern populations often ignore aristocracy (except in the case of tabloid coverage), many words once used for royalty are now unusual and obscure. Such is the case with liege. If you refer to someone as "my liege" you are probably playing a game.
Ah, the Medieval era, where we find the word liege as we know it, a term used by underlings for the lord of their land. The word was probably of Germanic origin, derived from the Medieval Latin laeticus. In an interesting etymological twist, the word at one time meant a leader of a band of free men — pretty much the opposite of its eventual meaning as a feudal lord. The word is not used much today, except in jest (see Python, Monty).