A square is a quadrilateral because it meets the defining criteria of a quadrilateral: it is a closed polygon with exactly four sides and four vertices. The term "quadrilateral" itself means "four sides," and a square has four straight sides

. More specifically, a square is a special type of quadrilateral with these properties:

• It has four sides of equal length.
• It has four right angles (each 90 degrees).
• Its opposite sides are parallel.
• The sum of its interior angles is 360 degrees, which is true for all quadrilaterals

Thus, since a square has four sides and satisfies the basic properties of quadrilaterals, it is classified as a quadrilateral. It is also a regular quadrilateral, meaning all sides and angles are equal, making it a highly symmetrical and special case within the quadrilateral family