The adjective ventral refers to the area on the body in the lower front, around the stomach area. The ventral fin on a fish is the one on its belly.
The ventral area of anything, plant or animal, is its underside. In directional terms, the ventral side is the area forward from (or under) the spinal cord. The word comes from the Latin noun venter, which meant "belly," which lent its meaning to ventrālis, which referred to anything pertaining to the belly area. When a shark is swimming toward you, you see the dorsal fin on its back but not the ventral fin on its belly, which remains unseen beneath the waves.
