Studying Shapes in Math

The Rectangle

The Rectangle: A rectangle is a quadrilateral that has four right angles.  The opposite sides are parallel.

The Rhombus

A rhombus is a four-sided shape where all sides have equal length.
Also opposite sides are parallel and opposite angles are equal.
Another interesting thing is that the diagonals (dashed lines in second figure) of a rhombus bisect each other at right angles.

The Square

A square has equal sides and every angle is a right angle (90°)
Also opposite sides are parallel.

The Parallelogram

Opposite sides are parallel and equal in length, and opposite angles are equal (angles "a" are the same, and angles "b" are the same)

The Trapezoid

Trapezoid	Isosceles Trapezoid

A trapezoid (called a trapezium in the UK) has one pair of opposite sides parallel.
It is called an Isosceles trapezoid if the sides that aren't parallel are equal in length and both angles coming from a parallel side are equal, as shown.

Language Note: In the US a "trapezium" is a quadrilateral with NO parallel sides!