A submarine canyon is a steep-sided valley cut into the sea floor of the continental slope, sometimes extending well onto the continental shelf, having nearly vertical walls, and occasionally having canyon wall heights of up to 5 km, from canyon floor to canyon rim.

Just as above-sea-level canyons serve as channels for the flow of water across land, so it is commonly held that submarine canyons serve as channels for the flow of turbidity currents across the ocean floor.