any of the stratified zones in the ocean which reflect sound during echo sounding, usually composed of marine organisms which migrate vertically from c. 250 to 800 m (c. 820 to 2,625 ft)
deep scattering layer in American English
noun
Geography
a zone of biological origin within the ocean, at a depth of 900–1200 ft. (270–360 m), which scatters sounding echoes