A "tail" is a flexible, elongated structure that extends from the rear of many animals, including mammals, reptiles, and birds. It serves various functions, such as balance, communication, and locomotion. For example, a cat uses its tail for balance while climbing, while a dog may wag its tail to express excitement or friendliness. In addition to animals, the term "tail" can also refer to the rear part of an object, such as the tail of an airplane, which helps with stability during flight. In astronomy, a comet's tail is formed by gas and dust that is released as it approaches the sun, creating a glowing trail in the sky.