Carinae, also known as the keel, refers to the central ridge of a boat or the central bump on the ventral side of some animals. Other words that can be used to describe this feature are ridge, crest, apex, spur, edge, and protrusion. In nautical terminology, the keel is also referred to as the backbone or spine of a boat. In biology, other terms that are often used synonymously with carinae include carinas, ridges, tors, ribs, and keels. The usage of these words primarily depends on the context in which they are being used, but they all refer to a prominent and central protruding feature.