golden section 
noun
The division of a line so that the whole is to the greater part as that part is to the smaller part (i.e. in a ratio of 1 to 1/2 (√5 + 1)), a proportion which is considered to be particularly pleasing to the eye.Both shank and line are in turn struck through by a diagonal, recalling the harmonious proportions of a golden section....
- Among his most prized possessions were his books of Plato, including the Timaeus in which the mathematical ratios of the golden section are described.
- So the phi by phi squares are themselves divided at their own golden section ratios by the side of the other overlapping square.