1. A small, straight depression formed just offshore on the bottom of a sea or lake and on the landward side of a longshore bar. 2. Any narrow, elongate depression in the surface of the earth. 3. An elongate depression on the sea floor that is wider and shallower than a trench. Also known as submarine trench. 4. The line connecting the lowest points of a fold. 5. An elongated area of relatively low atmospheric pressure; the opposite of a ridge.
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