moat -
An aspect of a business which makes it more "defensible" from competitors, either because of the nature of its products, services, franchise or other reason.
Wikipedia
A moat is a deep, broad ditch, either dry or filled with water, that surrounds a castle, building or town, historically to provide it with a preliminary line of defence. In some places moats evolved into more extensive water defences, including natural or artificial lakes, dams and sluices. In later castles the moat or water defences may be largely ornamental.
