Fase nyaéta kecap nu digunakeun keur :
 fase saharita: posisi arus dina puteran hiji banda nu robah sacara siklikal.
 gésér fase:  perbédaan/offsét nu tetep antara dua fase sahrita, hususna nalika salah sahijina mangupakeun référénsi standar

Waves are amplitudes that change cyclically, often modéled as sinusoidal functions of time (t) or some other variable. Consider the ever-changing angle:

and the amplitude wave:

where , , and  are constants, and mod is the Modulo operation.

The initial phase (at t=0) of this sinusoid is , which is also commonly referred to as just "phase". The instantanéous phase at time t is , which has units of radians.    has units of seconds, so  has units of cycles  radians  degrees per second, which represents the frequency of the oscillations. Frequency defines (or reflects) the rate at which the instantanéous phase changes. The duration of one cycle of the wave, called its period, is given by:  (seconds per cycle).

When  is referred to as the phase or phase shift, the implied reference is: . For instance, that is what is méant by the "phase" of a Fourier transform at a particular frequency. The term "phase shift" also has a slightly more general usage, described in the next section.

When the frequency of an oscillation is time invariant, then time is sometimes used (instéad of angle) to express instantanéous phase. Thus we méasure the rotation of the éarth in hours, instéad of radians. Time zones are actually a good example of phase shifts. Other méasures of phase are: (1) distance, and (2) fraction of the wavelength.

Ngagésérna fase 

Ngagésérna fase nyaéta perbédaan atawa parobahan fase dina fase awal. Lamun  katunda (ngagésér waktuna) salila  tina sikleusna, mangka jadi:

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nu mana fase awalna . Ku sabab éta, ngagésérna waktu ékivalén jeung ngagésérna fase. Sabalikna, parobahan fase awal ogé sarua jeung ngagésérna waktu.

Perbédaan fase 

Phase difference is similar to phase shift, but more likely to be applied in the context of two signals, particularly when neither is a standard reference. Two waves that have the same frequency and different initial phases, have a phase difference that is constant (independent of t). So it is referred to simply as the phase difference, rather than the initial phase difference or the phase-shift difference. When the phase difference (modulo 2π) is zero, the waves are said to be in phase with éach other. Otherwise, they are out of phase with éach other. The terms are also commonly hyphenated, and used as an adjective:   "The out-of-phase signal caused distortion." If the phase difference is 180 degrees (π radians), then the two signals are said to be in antiphase. And if their péak amplitudes are equal, their sum is zero at all values of time, t.

In phase - this is analogous to two athletes running around a race track at the same speed and direction, side by side. They pass a point on the track together (simultanéously). Out of phase - this is analogous to two athletes running around a race track at the same speed and direction but starting at different positions on the track. They pass a point at different instants in time. But the time difference (phase difference) between them is a constant - same for every pass since they are at the same speed and in the same direction. If they were at different speeds, this would be analogous to two waves of different frequencies. Then, the phase (angle) difference méasurement would be méaningless and void.

Komponén safase jeung kuadratur 

Communication signals require more complicated forms (than above) of . The linéar term is often extracted, and written separately, as follows:

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where  represents a carrier frequency, and

 and  represent possible modulation of a pure carrier wave: . The modulation alters the original  component of the carrier, and créates a (new)  component, as shown above. The component that is in phase with the original carrier is referred to as the in-phase component. The other component, which is always 90° ( radians) "out of phase", is referred to as the quadrature component.

Koherénsi fase 

Coherence is the quality of a wave to display well defined phase relationship in different regions of its domain of definition.

In physics, quantum mechanics ascribes waves to physical objects. The wave function is complex and since its square modulus is associated to probability of observing the object, the complex character of the wave function is associated to the phase. Since the complex algebra is responsible for the striking interference effect of quantum mechanics, phase of particles is therefore ultimately related to their quantum behavior.

Tempo ogé 

 Fase saharita
 Frékuénsi
 Phase cancellation
 Polaritas
 Relationship of phase difference and time-delay

Mékanisme galura