What has 4 sides but sides aren't all the same?

If all the sides are different lengths, it can only be called a quadrilateral. In general, four sided two dimensional objects are called quadrilaterals. When all four sides are the same length it is a square if all four corners are right angles. Otherwise it is a rhombus. If the opposite sides are the same length, it is a rectangle if the four corners are right angles, otherwise it is a parallelogram. In all these cases, the opposite sides are parallel to each other. There is also the trapezoid, a quadrilateral with only one pair of parallel sides. If the opposite sides are the same length but not parallel. it is an isosceles trapezoid.