An isosceles trapezoid (isosceles trapezium in British English) is a quadrilateral with a line of symmetry bisecting one pair of opposite sides. This pair of sides is parallel. This makes it automatically a trapezoid. A rectangle is a special case of the isosceles trapezoid, where it doesn't matter which pair of sides you use.
The diagonals of an isosceles trapezoid are congruent and intersect at equal positions.
