A quadrilateral is a polygon with four sides. It is characterized by having four vertices (corners) and four angles.
Polygon: A polygon is any closed figure with straight sides. Quadrilaterals are one type of polygon.
Parallelogram: A parallelogram is a special type of quadrilateral where opposite sides are parallel.
Trapezoid: A trapezoid is another type of quadrilateral with only one pair of parallel sides.