A window includes: a substrate including a folding area, a non-folding area, an upper surface, and a lower surface, wherein the folding area is configured to fold about a folding axis; and a plurality of groove patterns arranged in the folding area along a first direction crossing the folding axis, wherein each of the plurality of groove patterns includes: a bottom surface recessed from the upper surface of the substrate and substantially parallel to the upper surface of the substrate; and a side surface, wherein each side surface of the plurality of groove patterns connects each bottom surface of the plurality of groove patterns to the upper surface of the substrate, and wherein the side surface includes at least one curved surface.