The rear, elongated part of many animals, extending beyond the trunk or main part of the body. Tails are used variously for balance, combat, communication, mating displays, fat storage, propulsion and course correction in water, and course correction in air.
A long, stream of gas or dust forced from the head of a comet when it is close to the Sun. Tails can be up to 150 million km (93 million miles) long, and they always point away from the Sun because of the force of the solar wind. ◇ Plasma tails, or ion tails, appear bluish and straight and narrow, and are formed when solar wind forces ionized gas to stream off the coma. Dust tails are wide and curved, and are formed when solar heat forces trails of dust off the coma; solid particles reflecting the Sun's light create their bright yellow color.