Prisms, on the other hand, have a third dimension. For example, if you start with length and width in two dimensions, to make a prism you have to give the shape height as well. If the shape has height and breadth, then it needs depth as well to be a prism. A prism also has two ends, all faces, exactly the same, which usually give it its name. For example, a triangular prism has two identical triangular ends. Some examples of other prisms are cubes, cylinders, and all sorts of boxes.

All prisms have one or more rectangular sides, joining up the two dimensional end shapes. So a sphere, which is the shape of a ball, isn’t classed as a prism, because it contains no rectangular sides. But a cylinder is a circular prism. If you cut down the side between the circular faces and unfold it, it’s a single rectangle. If we unfold any prism, we can see that one or more rectangles form the sides, and then we can see the shape of the ends which determine the name of the prism.

This is a triangular prism. If all the sides are rectangular, then it’s called a rectangular prism. Most boxes are rectangular prisms.