PhiPhi (uppercase Φ, lowercase φ) is the name of:
- The 21st letter of the Greek alphabet (unrelated to ordinality but rather to linguistics, it's associated with letter f in the Latin alphabet).
- In engineering, the diameter symbol is often referred to as "phi". This symbol is used to indicate the diameter of a circular section, for example means the diameter of the circle is 14 inches or millimeters, depending on the context.
- The Greek letter used to represent the so-called Golden mean and the Euler totient function.
- In spherical coordinates phi is usually used to represent the angle to the z axis.
- The golden mean (1+√5)/2 is often called Φ, φ being 1/Φ.
See also: Phi phenomenon.