noun: frequent changes in the amount, value, or level of something
noun: the quality of being unsteady and subject to fluctuations ("He kept a record of price fluctuations")
noun: a wave motion ("The fluctuations of the sea")
noun: an instance of change; the rate or magnitude of change
In quantum physics, a quantum fluctuation (or vacuum state fluctuation or vacuum fluctuation) is the temporary change in the amount of energy in a point in space, as explained in Werner Heisenberg's uncertainty principle.
This allows the creation of particle-antiparticle pairs of virtual particles. The effects of these particles are measurable, for example, in the effective charge of the electron, different from its "naked" charge.
Quantum fluctuations may have been very important in the origin of the structure of the universe: according to the model of expansive inflation the ones that existed when inflation began were amplified and formed the seed of all current observed structure. Vacuum energy may also be responsible for the current accelerating expansion of the universe (cosmological constant). Wikipedia, Quantum Fluctuation
Rhythmic Balanced Interchange
8.3 - Conventional View of Wave Motion