The golden ratio is a proportion (roughly 1:1.6) that occurs frequently throughout the natural world and is applied across many areas of human endeavor including engineering, architecture, art, interface design and music. The golden ratio, also known as the golden mean, the golden section or the divine proportion, is symbolized as the Greek letter phi.
In mathematical terms, the golden ratio is an irrational number: 1.61803398874989484820... repeating without a pattern to thousands of decimal places. The ratio is closely related to the Fibonacci sequence, also frequently observed in the natural world and used to gude design. Any two sequential Fibonacci numbers, such as eight and thirteen or thirteen and twenty-one, demonstrate a ratio very similar to the golden mean.
In IT (information technology), the golden ratio is often used to guide website, user interface (UI) and user experience (UX) design. Studies of the phenomenon have indicated that humans can scan images and take in the information more quickly when it is presented in a golden rectangle, with length-wise sides roughly 1.6 times as long as vertical sides. People tend to find golden rectangles more pleasing to look at than others.
See an introduction to the golden ratio: