It's just an old form of address to a superior, usually a master of the house or similar. Very similar to: Your Majesty; The Right Honourable Gentleman; etc.

I saw it in wikipedia, Shadowar, but the words used by them to explain the meaning are very complex to me to understand. =/ But thanks, anyway.

according to wikipedia In the nineteenth century, milord (also milor) (pronounced "mee-lor") was well-known as a word which continental Europeans (especially French) whose jobs often brought them into contact with travellers (innkeepers, guides, etc.) commonly used to address Englishmen or male English-speakers who seemed to be upper-class (or whom they wished to flatter) – even though the English-language phrase "my Lord" (the source of "milord") played a somewhat minor role in the British system of honorific forms of address, and most of those addressed as "milord" were not in fact proper "lords" (members of the nobility) at all. The word "milord" was occasionally borrowed back into the English language in order to be used as a sarcastic or jocular reference to British travellers abroad. (Most English-speaking tourists in the 1700s had to be rich to undertake the "Grand Tour".) The most famous usage in recent years has been the 1959 French song "Milord" by Edith Piaf see on en.wikipedia.org/wiki/Milord

"Milord" is like "my lord" as a form of address of an English gentleman, but is also used as a noun.