A rectangle is any shape with four sides and four right angles. All squares are rectangles but not all rectangles are squares (all the sides in a square have to be the same length).
The rect in rectangle comes from the Latin rectus, which means "right" or "straight." Because of its right angles, a rectangle has straight sides. Another word with the same root is rectitude, which means moral uprightness. A morally upright person is someone who does the right thing, but doing the right thing doesn't make you a square — or a rectangle.
