The seabed is the ground at the bottom of the sea — the land under all that water. People also say sea floor or ocean floor; they mean the same place. Scientists talk about the seabed when they study the sand, mud, rocks, plants, and animals down there, or when they look for oil and cables. Ships drop their anchors onto it. Though actually it is not one flat bed of sand: there are mountains, valleys, and thick mud, just like on land, only hidden. The word is ordinary in news about the sea, a little school-science in class.

海床（口語也常說海底）