RS Aggarwal Solutions for Class 8 Chapter 15 "Quadrilaterals", it means "four sides" (quad means four, lateral means side). A Quadrilateral has four-sides, it is 2-dimensional (a flat shape), closed (the lines join up), and has straight sides. In Euclidean plane geometry, a quadrilateral is a polygon with four edges and four vertices. Other names for quadrilateral include quadrangle, tetragon, and 4-gon. Quadrilaterals deals with the definition of quadrilaterals, sides, vertices and angles of quadrilaterals. It also covers some basic definitions like adjacent sides of a quadrilateral, opposite sides of a quadrilateral, adjacent angles of a quadrilateral, opposite angles of a quadrilateral and angle sum property of a quadrilateral.