A cuboid has 8 corners, 12 edges, and 6 faces. Lines can be straight or curved, with straight lines being vertical, horizontal, or slanting. Closed shapes that do not cross themselves are simple closed curves. Polygons are closed shapes formed only with straight lines. Polygons are named according to the number of sides, with a 3-sided shape called a triangle and a 4-sided shape called a quadrilateral. A rectangle has opposite sides of equal length and a square has 4 equal sides.