Phi (Φ φ) is the 21st letter of the Greek alphabet and has a numeric value of 500.
The lower-case letter φ is used as a symbol for:
- Euler's phi function φ(n)
- The golden mean.
- In physics and mathematics, the value of an angle.
- The work function.
- The empty set.
- In signal processing, the phase of a sinusoidal signal.