Wave Particle Duality
A wave is the propagation of a disturbance, which causes a reversible variation of physical properties on its way. For instance, sea waves influence water levels. In quantum mechanics, fundamental particles may in certain cases be assimilated to waves, and vice versa. This property of quantum objects explains why the elementary grain of light, the photon, can behave both as a wave and as a particle. Depending on the circumstances, one or the other of these two aspects will be put to the fore.