What is a "back door" front?

I have been eyeballing a possible "back door" cold front for Thursday. It may just barely make it through for a time, or it may pull the trick that sometimes happens just ahead of it.. with lighter winds, the coast, esp. from Boston up to Newburport, flips into a seabreeze even AHEAD of the front before it moves by. It is called a back door front because it drops down from the north, taking the back door in, rather than the normal side/front door from the Ohio valley. Even if it does move in for a time, it will bounce right back out Thu. night making for a warm Friday start before that cold cold finish. (with rain in between)