An n-gon is a polygon with "n" sides, where "n" is a placeholder for any number. The letter "n" is commonly used alongside other letters in mathematics and science as variables to represent unknown numbers.
According to About.com, "a polygon is a closed shape and is formed by line segments." This means that the shape must not have any holes or breaks in its outline, and there can be no curved lines. A polygon is also two-dimensional, meaning it does not have depth. For example, a square is a polygon, whereas a circle and a cube are not. A polygon must have the same number of corners as it does sides.