Why are three dimensional shapes called that?

Answer 1

Short Answer: There are 3 coordinates which are needed to describe any point on the shape.

Longer Answer:

Think of the dimension being a direction an object can be described in, whether negative or positive.

A 1-D (one dimension) object only needs one number to describe its location. Using the coordinate system most people know (Cartesian) lets call this direction x.On a 1-D object your location out be (x).

With a 2-D object you now are adding a y coordinate to the x coordinate. To describe where you are on a 2-D object you need both the x and y coordinate. Your location would be (x,y)

3-D adds yet another coordinate to the mix: z. Now to describe position in 3-D space you need all three coordinates (x,y,z). To describe a 3-D shape you will also need all three coordinates. This is the reason that 3-D shapes are called 3-D shapes, because of the need for the x, y, and z components needed to describe any point on the shape.