A stack of identical polygons will make a prism.A stack of polygons which gradually become smaller will make a pyramidal frustum.
If the stack continues until the polygon becomes infinitesimally small, then they will make a pyramid.
Under the same conditions, discs will make a cylinder, conic frustum and cone, respectively.
Since any polygon can be constructed from a combination of other polygons, I would call this rule a "trivial property of polygons".
pyramid (not including the vertex) Prism
A polygon is pretty much any enclosed shape constructed of straight line segments connected end to end. The angles do not have to be right. In fact, they usually aren't. A right angle would NEVER be a polygon, as it is just one right angle. In Euclidean geometry a right angle must be accompanied by two acute angles to form a triangle--the polygon with the smallest number of sides.
A polygon is a 2-dimentional polytope. The polytope extends the idea out of the plane (the 2 dimensions in which a polygon is confined), and is a more general term. A polygon is a planar geometric figure constructed using 3 or more line segments that are joined end to end to end. The segments make a "closed" figure by virtue of the fact that they are each and every one connected end to end to end. Wikipedia has a good post on the polygon. You'll find a link to that post just down below here. Surf on over, even if it's just to look at the diagrams there. It will be worth the trip simply to see the figures.
The definition of a irregular polygon is any polygon that is not a regular polygon.
a cone (not including the vertex) and a cylinder
The constructed polygon name for a 24-sided regular polygon is an icosikaitetragon.
Since any polygon can be constructed from a combination of other polygons, I would call this rule a "trivial property of polygons".
A diamond is indeed a polygon. It's a closed figure lying on a plane and constructed of straight lines.
This is called a frequency polygon.
More complicated polygons.
A Zamboni pile is an early electric battery constructed from discs of silver foil, zinc, foil and paper.
An equilateral triangle, a square and a hexagon.
A bell is a shape, but not a polygon. Polygons are constructed only from straight line segments, they do not contain curves (a circle is not a polygon either, unless you imagine it as being composed of infinitely many line segments, each of which is infinitely short).
Any 5 sided shape constructed from straight non overlapping lines. A 5 sided polygon.
pyramid (not including the vertex) Prism
Cone ( not including the vertex ) Cylinder ( APEX )