Two-dimensional (2-D) shapes are all around you. There are regular and irregular 2-D shapes, which are both used in art including sculptures, mosaics, and paintings. One special pattern is a tessellation, which has shapes that fit together with no gaps in between. Many pieces of artwork and architecture use lines of symmetry-one side is exactly like the other. Another special pattern is a tangram, which is a puzzle in which there are different shapes that form a square.