What do you call a polygon with four sides, none of which are the same size?

In general, a shape with four sides, whether they are equal or not, is called a quadrilateral. Another name for this type of shape is a tetragon.

A polygon that does not have equal sides has a special name, an irregular polygon. However, that name can be applied to a polygon that has any number of sides, as long as the sides don't match up. Therefore, a polygon with 12 sides could be an irregular polygon. Alternatively, an irregular polygon can be one that does not have matching angles, such as a concave polygon, whether or not pairs of the sides are equal in length.