Naming 2D shapes

The circle is kept on the page because it is the shape that breaks the rule: no straight sides and no corners at all, only one curved edge, and seeing it beside the others is what makes the word “side” mean something. The four-sided shapes are the other place to slow down — square, rectangle, rhombus, and trapezoid all have four sides, so the count alone does not tell them apart. The drawing does, and the quadrilateral family chart is where that difference becomes a rule.