The term duck can refer to a bird that belongs to the Anatidae family, which includes mallards, pintails and other species. It is also used as a verb to mean to dodge or evade something, such as an attack or responsibility. In addition, "duck" can be used in various idiomatic expressions, including "sitting duck," meaning someone who is vulnerable or defenseless, and "blowing off steam like a duck", which means to release tension through physical activity.