Quadrilaterals One pair of parallel sides Trapezium Two pairs Two pairs of equal of equal parallel adjacent sides sides Kite Parallelogram Four sides equal Four right angles Rhombus Rectangle Four right angles Four equal sides Square Legend Quadrilaterals A, B, C, D are angles a, b, c, d are side lengths B All sides in one plane Not all sides in one plane b Skew a C Planar c A D No crossed sides d Two crossed Note that all properties are sides Simple inherited along the arrows All angles < 180° Complex One angle > 180° Arrow Antiparallelogram (Self-intersecting) Concave (aka Dart/Chevron) Convex Two pairs of Two pairs of opposite equal adjacent equal sides sides Opposite angles sum to 180° Opposite side One pair Equal One pair lengths have Perpendicular of parallel diagonals of opposite equal sums diagonals sides equal sides Tangential Watt Cyclic Ex-tangential Orthodiagonal A + C = B + D = 180° (Inscriptible) a + c = b + d 2 2 2 2 Trapezium Equidiagonal a + c = b + d quadrilateral a + c = b + d A + B = C + D = 180° One pair of Opposite side lengths parallel ides Non-equal Two pairs of equal have equal sums opposite adjacent sides sides parallel Two One pair of Non-parallel Two pairs A second adjacent parallel sides Opposite of equal sides equal (if circle r=∞) pair of parallel right sides Opposite adjacent sides angles equal sum angles sides equal sum Right-angled Isosceles Kite Tangential Parallelogram Bicentric (‘Rhomboid’ if adjacent trapezium trapezium sides are unequal) trapezium Two Four sides Four Four sides Four right Four Four right One pair of opposite equal sides equal angles right angles opposite right equal angles equal sides angles Opposite side Third lengths have equal sums side equal Four right angles Right kite Rhombus Quadric Rectangle 3-sides-equal Isosceles (‘Oblong’ if adjacent trapezium tangential sides are unequal) Four right angles Four Four equal equal sides Four right angles sides Four equal sides Square Equilic 60° .