Phi (noun)

1. The 21st letter of the Greek alphabet, used to represent various values and concepts in mathematics, science, and engineering, including the golden ratio.
2. A mathematical constant that is approximately equal to 1.61803398874989, represented by the Greek letter phi (φ). It is an irrational number that is found in many natural phenomena, including the shapes of certain crystals and the ratio of certain distances in the human body.

Origin:

Late 19th century: symbol, denoting the golden ratio (1.61803398874989…), from greek phi, the initial letter of philetairos "loving one"s friends".

Examples:

1. The ratio of the Fibonacci numbers converges to the golden ratio, denoted by the Greek letter phi.
2. The Fibonacci sequence is closely related to the golden ratio, often denoted by the symbol phi.
3. The phi is a very important number in art, architecture, and design.
4. The phi is used in the design of logos, websites, and other visual elements.
5. The ratio of consecutive Fibonacci numbers approaches phi as the Fibonacci numbers become larger.