continental shelf

noun

a submerged shelf of land that begins at a continental shoreline, slopes downward gradually at an angle of about 0.1° for a variable distance, and ends at the top of a much steeper downward slope (continental slope) at an angle of about 3° to 6° until it reaches the ocean floor: at the outer edge of the shelf the depth of the ocean is usually between about 90 m (300 ft) and 180 m (600 ft)