noun: An expanse of an ocean, sea, or large lake which is distant from shore and devoid of nearby islands or other obstructions.
noun: In a river, pond, or other small body of water, an area of surface unobstructed by aquatic vegetation, boulders, and the like, adequate for navigation or swimming.
noun: (chiefly Canada) An area of an ocean, sea, lake, or river which is not covered by ice.