The digon is the degenerate polygon (corresponding to a line segment) with Schläfli
symbol 
.
In the illustration, the two polygon edges of the digon coincide with the line segment 
and therefore appear as a single line
segment.
Digon
See also
Dihedron, Full Angle, Hosohedron, Line Segment, Polygon, Trigonometry Angles--pi/2Explore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Digon." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Digon.html