Phase
The fractional position of a point within a wave cycle, expressed as an angle relative to a reference origin.
Governing formula
Φ(x,t) = k x - ω t + φ0
SI unit
rad (radians)
In depth
Phase specifies whether a point on a wave is at a crest, trough, or zero crossing at a given instant.
Examples in the real world
Two waves with a phase of 0 or 2π are completely in phase, while a phase of π represents complete opposite phase (out of phase).