Quadrilateral with two sides (bases) that are parallel. It is isosceles when it has two sides that are not parallel and equal, and rectangle when two of its sides form a right angle.

rectangle

Quadrilateral whose opposite sides are equal in length; the sides meet at right angles.

square

Equilateral rectangle with four right angles.

rhombus

Equilateral parallelogram.

triangle

Three-sided polygon; triangles are scalene (no side is equal to any other) isosceles (two sides equal) or equilateral (all sides equal).