It's called the Benthic Zone, though this name can apply to deep lakes as well as oceans.
Conglomerate rock
abyssal plain
seamont ?
continental margin deep-ocean basin
benthic realm
oceanographer
Challenger Deep.
The Marianas trench .
Wreck debris or a debris field
An ancient under sea valley carved in the ocean floor is known as a canyon, usually given the name of the contributory river on the land. such as the Hudson Canyon, or the Clutha Canyon.
Sea floor spreading
Icebergs float in the Southern Ocean, and in the Arctic ocean.