A quadrilateral is simply a four-sided polygon. In general, quadrilaterals may be classified as regular (having all sides congruent and all angles congruent) or non-regular (a variety of side lengths and angle measures). They may be convex (all interior angles less than 180 degrees) or concave (one or more interior angles greater than 180 degrees). In this topic, you will study five types of quadrilaterals – parallelograms, rectangles, squares, rhombuses and trapezoids. You will explore and apply the properties of each of these quadrilaterals and apply them to real world situations. You will find that there are some common characteristics among these four-sided figures.