phi
n. countable C1 Advanced US //ˈfaɪ// UK //fˈaɪ// phi
n. the Greek letter φ, used in math and science to show a special number or value.
n. the twenty-first letter of the Greek alphabet; in technical contexts, it denotes the golden ratio, electric potential, or a specific statistical measure.
The symbol phi represents the golden ratio.
Engineers use phi to calculate the stress on the bridge.
In classical physics, phi often denotes the phase angle in wave equations.