Quadrilaterals are four-sided shapes that are found in many areas of mathematics. They have four angles and four sides that are all connected. In geometry, many types of quadrilaterals exist including parallelograms, rectangles, squares, trapezoids, rhombuses and kites. Quadrilaterals can also be classified by the length of their sides, such as an isosceles trapezoid or an equilateral rectangle. Additionally, quadrilaterals can be used in trigonometry to calculate angles and distances. Quadrilaterals can also be used to solve equations and simplify complex problems. Understanding quadrilaterals is essential for students studying math, from elementary school all the way through college.