They have one fewer dimension; they lack depth.
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Perimeter is a concept which is relevant to closed 2-dimensional shapes, not 3 dimensional objects.
The difference is that two-dimensional shapes have a length and a width while three-dimensional shapes have a length, width, and depth. While some examples of two-dimensional shapes are circle, rectangle, and triangle, example of three-dimensional figures are a sphere, cuboid, and a pyramid.
Polygons !
You can't. Volume is only for 3 dimensional shapes. You won't find a way of using volume in any kind of 2 dimensional stuff.
The three dimensional figures are called Space figures