Two examples of parallelograms seen in everyday life are the United States Postal Service symbol and the intricate structures on the neck of a guitar. A parallelogram is a quadrilateral with both pairs of opposite sides being parallel.

There are many shapes that can qualify as being parallelograms. A rectangle is a parallelogram with all four interior angles measuring at 90 degrees. A rhombus is a parallelogram with all four sides being equal in length. A square is a parallelogram with all four sides equal in length and all interior angles measuring 90 degrees. A quadrilateral is considered a parallelogram if it fits three criteria. Both pairs of opposite sides must be parallel. Both pairs of opposite sides are congruent. If they are congruent, they will also be parallel. One pair of opposite sides are congruent and parallel. If this is true, then the other pair of opposite sides is parallel.

A parallelogram has several properties that are related to its base, altitude, area, perimeter, opposite sides and diagonal. The opposite angles of a parallelogram are equal. Consecutive angles of a parallelogram are supplementary, meaning their sum is equal to 180 degrees. Linking the midpoints of each side of a quadrilateral results in the formation of a parallelogram.