What kind of polygon is an arrow?

This question is very difficult to answer because of the ambiguity of what an "arrow" is. An arrow that you might fire from a bow is a three dimensional object and so is not a polygon. An arrow drawn as a straight line with a direction indicator at its head with or without tail feathers (for example <|----<< : oh, the graphics on this browser are so good, aren't they!) is not a polygon because the shaft is a line: a 1-dimensional object. An arrow such as the default one used to represent the cursor in Windows is a concave heptagon.