A convex quadrilateral is a four-sided figure with interior angles of less than 180 degrees each and both of its diagonals contained within the shape. A diagonal is a line drawn from one angle to an opposite angle, and the two diagonals intersect at one point.
The four vertices, or corners, of a convex quadrilateral point outward and away from the interior of the shape. Two common types of convex quadrilaterals are squares and rectangles. The area of an irregular quadrilateral can be determined by finding the area of the four triangles made by the intersecting diagonals. All regular quadrilaterals, which have the same angle for each vertex, are convex.