Gallon A measure of volume (liquid) that is equal to 4 quarts or 231 cubic inches or 3.7853 liters.

Geodesic Dome A geodesic dome is a spherical structure made up of triangles.  As you can see in the picture on the right, some triangle groupings form pentagons and some form hexagons.   If they all formed pentagons, then it would make an icosahedron which wouldn't be wide enough.  Some geodesic domes are huge.  A great example is the Montreal Biosphere.

Geometry Geometry is the science that studies the size and shape of things.

Golden Rectangle
The golden rectangle is a rectangle with very special dimensions...  To get the length, you multiply the width by the golden ratio (see definition above).   One very special property of the golden rectangle is that you can break it into a square and a smaller rectangle --  and that smaller rectangle is another golden rectangle!

                

The ancient Greeks found that the golden rectangle was very pleasing to the eye and used it in a bunch of their architecture (The Parthenon) and the artists of the Renaissance (like Leonardo DaVinci) used the golden rectangle in their paintings.