Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A polygonal chain, polygonal curve, polygonal path, or piecewise linear curve, is a connected series of line segments. In computer graphics a polygonal chain is called a polyline and is often used to approximate curved paths. A simple polygonal chain is one in which only consecutive (or the first and the last) segments intersect and only at their endpoints. A closed polygonal chain is one in which the first vertex coincides with the last one, or, alternatively, the first and the last vertices are also connected by a line segment. A simple closed polygonal chain in the plane is the boundary of a simple polygon. Often the term "polygon" is used in the meaning of "closed polygonal chain".