fog bank

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A dense mass of fog defined against clearer surrounding air, often as viewed from a distance at sea.

from The Century Dictionary.

• noun A term applied to a mist of condensing vapor of any liquid, not necessarily water, consisting in reality of an immense number of minute drops of the liquid in a state of suspension.
• noun A stratum of fog as seen from a distance.
• noun An appearance at sea in hazy weather, sometimes resembling land at a distance, but vanishing as it is approached: sometimes called by sailors Cape Fly-away, Dutchman's Land, and No-man's Land.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a large mass of fog on the sea (as seen from a distance)