1, definition of parallelogram: two groups of parallelograms with parallel opposite sides are called parallelograms.

2. Features of parallelogram: Two groups of opposite sides are parallel and equal respectively.

3. The base and height of the parallelogram: Draw a vertical line from a point on one side of the parallelogram to the opposite side. The line segment between this point and the vertical foot is called the height of the parallelogram, and the side where the vertical foot is located is called the bottom of the parallelogram.