A parallelogram is a four-sided shape, or quadrilateral, where opposite sides are both equal in length and parallel. This means that the two pairs of opposite sides never meet, no matter how far they are extended. Common examples of parallelograms include rectangles, squares, and rhombuses. In a parallelogram, opposite angles are also equal, and the adjacent angles are supplementary, meaning they add up to 180 degrees. The area of a parallelogram can be calculated by multiplying the base by the height. This property makes parallelograms useful in various fields, including geometry and architecture.