Since there is a (quantum) limit in the entropy by surface unit (for every four Planck areas there is at most one degree of freedom –or a entropy unit corresponding to a Boltzman constant): the maximum entropy contained in a volume bounded by a surface of area A (measured in Plank areas) is A/4, which is named holographic bound.

The holographic principle is related to the “generalized second law” [of thermondynamics], proposed by Bekenstein, stating that “the sum of black hole entropies and the ordinary entropy outside the black holes cannot decrease” (Bekenstein 2003).

By extension of the holographic principle, Bekenstein suggests that if the physics of our real universe (four-dimensional) were holographic, there would be an arbitrary set of physical laws to be applied on some three-dimensional bound of the space-time (i.e. the horizon of events).