n.
Extension of the vertebral column beyond the trunk, or any slender projection resembling such a structure.
In fishes and other animals living completely or partly in water, it is very important to movement through water. Many tree-dwelling animals (e.g., squirrels) use the tail for balance and as a rudder when leaping; in some (e.g., certain monkeys), it is adapted for grasping. Birds' tail feathers aid in flight maneuverability. Other animals use their tails for defense (e.g., porcupines), social signals (e.g., dogs and cats), warning signals (e.g., deer and rattlesnakes), and hunting (e.g., alligators).