In the Middle Ages, the area between England and Wales wherein Marcher lords had some degree of autonomy. It's definition today is somewhat looser, and refers to the area along the English border with Wales.
Fact of the Day
Elizabeth I could cost her hosts so much on her visits that some tried to shut up their houses and stay away to prevent it. This did no good for the earl of Lincoln: Elizabeth broke into his Chelsea residence, had a feast, and then charged the bill to Lincoln.