They are both quadrilaterals
With that fact we can come up with similarities:
Both have 2 pairs of parallel lines
Both have 4 right angles (Angles that measure 90°)
Both have 4 sides
Perimeters can be computed by adding all the sides.
Even if they are both quadrilaterals, they are not the same. A square has 4 equal sides. A rectangle is not a square, but a square is considered to be a special rectangle.