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.