A deep, wide defensive ditch, normally filled with water, surrounding a fortified habitation.

(business, figurative) An aspect of a business which makes it more "defensible" from competitors, because of the nature of its products, services or franchise or for some other reason.

A circular lowland between a resurgent dome and the walls of the caldera surrounding it.

(meteorology) A clear ring outside the eyewall of a tropical cyclone.

(transitive) To surround with a moat.