8th Grade FAST Mathematics Pre-Algebra Practice Test

A quadrilateral is a four-sided polygon. That means it’s a closed figure made up of four straight sides and four vertices. The simplest, most direct description of a quadrilateral is simply “a four-sided polygon,” because that captures both the four-side count and the polygon nature.

If something has only three sides, it’s a triangle, not a quadrilateral. If it has five or more sides, it’s a pentagon or a higher polygon, not a quadrilateral. If a figure is closed and all its interior angles are 90 degrees, that describes a rectangle (a specific type of quadrilateral), which shows that a quadrilateral can come in different forms. But the general idea behind a quadrilateral is being four-sided, which is why the direct description fits best.