Animation without computers, which is now often called “traditional” animation, has a long and rich history of its own which is continuously being written by hundreds of people still active in this art. Animation is derived from the Latin anima and means the act, process, or result of imparting life, interest, spirit, motion, or activity. Motion is a defining property of life and much of the true art of animation is about how to tell a story, show emotion, or even express subtle details of human character through motion. While overlapping is necessary to keep the motion natural, secondary action is often added by the animator to make motion more interesting and achieve realistic complexity of the animation. The term keyframing can be misleading when applied to 3D computer animation since no actual completed frames are typically involved. Natural motion rarely happens along straight lines, so this should generally be avoided in animation and arcs should be used instead.