Sometimes they are.
It depends on the context of the sentence. Squares may be considered as a special case of rectangles. Alternatively, the term rectangles may be reserved for right-angled quadrilaterals other than squares.
Parallelograms are squares is sometimes true. Squares are parallelograms is always true. Rhomboids are parallelograms is also always true. So not all parallelograms are squares but some are.
No, they are NEVER rectangles.
Some polygons are rectangles. The vast majority are not.
This is a little odd, but: All squares are rectangles, but rectangles are never squares.
A parallelogram is any quadrilateral in which both sets of opposite sides are parallel, or will never intersect. Squares and rectangles (both quadrilaterals) satisfy that condition, and so would rhombus.
Some parallelograms are squares - the ones which are equiangular (have equal angles) and are equilateral (have equal side lengths). All squares are parallelograms, but only some parallelograms are squares.
Rectangles and squares are quadrilaterals, or a polygon* with four sides. Rectangles have two sets of parallel** sides. Squares have four sides of equal length and four right angles*** for the corners. Rectangles and squares are not the same thing. * Polygon- a closed figure with straight sides. ** Parallel- two lines, that no matter how far they stretch, will never meet each other. *** right angles- a 90 degree angle.