A trapezoid is a four-sided shape that has only two parallel sides. Most quadrilaterals have two pairs of parallel sides for four sides total, such as squares, rectangles, rhombuses and parallelograms.
A trapezoid is defined by having only one pair of parallel sides. None of the sides are required to be the same length, and the two non-parallel sides can be at any physically possible angles. The perimeter can be calculated by adding together the length of the sides. The formula for the area of a trapezoid is (a+b)*h/2, where "a" and "b" are the length of the parallel sides, and "h" is the distance between those sides.