A stretched thread, the path of an ant, the outline of a cloud: these are all lines. Some are straight, others curve. Straight and curved, open and closed A straight line does not change direction, like a tightly stretched string. A curved line changes direction all the time, like the path of a snake. A closed line ends where it began, like the outline of a circle. An open line has two loose ends. A line made only of straight pieces is a polygonal. When it is closed, it draws a polygon.