Trapezoids are not necessarily parallelograms, as a trapezoid only needs one pair of parallel sides, unlike parallelograms, which need two. However, there are two definitions of what a trapezoid is, and one of them considers parallelograms to be trapezoids.
In an isosceles trapezoid, the two sides that aren't parallel are the same length and have the same angles relative to the parallel sides. Using an inclusive definition of a trapezoid that allows both pairs of sides to be parallel, rectangles fall under the definition of a trapezoid and are isosceles. The exclusive version of the definition omits these shapes since both pairs of sides are parallel.