Quantum fluctuation

A quantum fluctuation is the temporary change in the amount of energy in a point in space, as explained in Werner Heisenberg's uncertainty principle. It applies only to quantum physics. 
That means that conservation of energy can seem to be violated, but only to allow the creation of virtual particle-antiparticle pairs for exceedingly short periods of time. Like normal matter and antimatter, theoretical electrons and positrons annihilate each other. Unlike normal matter, however, they do not create any energy when they annihilate each other, but instead create an imaginary photon. Normal photons can interact with matter, but theoretical photons do not.
References.
Abhyudaya Apoorva - The theory of nothing