text: In addition to everyone else, to illistrate the difference between 2-d and 3-d.  If you look at a wall, and forget about it having a fixed width, you currently see only 2 dimensions, a length, and a height.\n\nFor a 3-d object, have a look at an opened door, this door has the 2 dimension from before, a length, and a height.  It also has a 3rd dimension being the width.\n\nIn drawing, a 2-d wall\n\n-----\n|   |\n|   |\n-----\n\na 3-d box\n\n  -----\n /   /|\n----- |\n|   | |\n|   |/\n-----