A visible mark, such as a footprint, made or left by the passage of a person, animal, or thing, A constituent, such as a chemical compound or element, present in quantities less than a standard limit, The point at which a line, or the curve in which a surface, intersects a coordinate plane, intransitive verb_ To go along or follow (a path, for example), To ascertain the successive stages in the development or progress of, To copy by following lines seen through a sheet of transparent paper, adjective_ Occurring in extremely small amounts or in quantities less than a standard limit