Any flat surface of a three dimensional figure.

A quadrilateral with two pairs of two equal sides that are also adjacent; it can be a rhombus if all sides are equal.

Two lines in a plane that do not intersect.

A four-sided closed figure with opposite sides that are parallel and equal.

Two lines are perpendicular if they intersect, and all of the angles formed between the lines are 90° angles

A flat surface that extends infinitely in all directions.

A closed figure made up of line segments.

A closed figure with four sides.

A parallelogram with four 90° angles. (Note: it must always be true.)

A three-dimensional figure with six rectangular sides.

A parallelogram with four equal sides.

An angle formed by perpendicular lines; angle measuring 90°.

A three-dimensional figure.

Squares of the same size—used for measuring.

Figures on a plane.