This number [represented by the symbol at left] is also known as the golden section and is commonly accepted as an expression that describes the perfect proportions in architecture or anatomy. In mathematics and the arts, two quantities are in the golden ratio if the ratio between the sum of those quantities and the larger one is the same as the ratio between the larger one and the smaller. The golden ratio is a mathematical constant, approximately 1.6180339887.
Of course, not all of them are this serious, but they are fascinating. Link -via the Presurfer