The golden ratio (phi) represented as a line divided into two segments a and b, such that the entire line is to the longer a segment as the a segment is to the shorter b segment.
This image was created by Eisnel and is placed in the public domain.
The golden ratio, also known as the golden proportion, golden mean, golden section, golden number, divine proportion, or sectio divina, is an irrational number, approximately 1.618, that possesses many interesting properties.
Shapes proportioned according to the golden ratio have long been considered aesthetically pleasing in Western cultures, and the golden ratio is still used frequently in art and design, suggesting a natural balance between symmetry and asymmetry. The ancient Pythagoreans, who defined numbers as expressions of ratios (and not as units as is common today), believed that reality is numerical and that the golden ratio expressed an underlying truth about existence.