The abyssal zone is the pelagic zone that contains the very deep benthic communities near the bottom of oceans. Abyss is from the Greek word meaning bottomless sea. At depths of 4,000 to 6,000 meters (13,123 to 19,685 feet), this zone remains in perpetual darkness and never receives daylight. Its permanent inhabitants - for example, the Black swallower, tripod fish, deep-sea anglerfish, and the giant squid - are able to withstand the immense pressures of the ocean depths, up to 775 kilograms per square centimeter (76 megapascals or 4.92 long tons force per square inch). Many abyssal creatures have underslung jaws to sift through the sand to catch food. The deep trenches or fissures that plunge down thousands of feet below the ocean floor - for example, the midoceanic trenches such as the Mariana Trench in the Pacific - are almost unexplored. Only the bathyscaph Trieste has been able to descend to these depths. These regions are also characterized by continuous cold and lack of nutrients. The abyssal zone has temperatures around 2 to 3 degrees Celsius.

The area below the abyssal zone is the sparsely inhabited hadal zone. The zone above is the bathyal zone, and above that is the photic zone, in which the majority of ocean life exists.