Definition: The holographic principle is a mathematical principle that the total information contained in a volume of space corresponds to an equal amount of information contained on the boundary of that space. This dependence of information on surface area, rather than volume, is one of the key principles of black hole thermodynamics.
The holographic principle was originally developed in 1994 by Dutch Nobel laureate Gerard 't Hooft and (shortly thereafter) by Stanford physicist Leonard Susskind. (Susskind's approach was more directly applicable to string theory, while 't Hooft's was a more general statement of the principle.)
In 1997, this principle was applied by Argentinian physicist Juan Maldacena to develop the anti-de Sitter space/conformal field theory correspondence (AdS/CFT correspondence), which demonstrated a connection between a 5-dimensional anti-de Sitter space (described by string theory) and its boundary, a 4-dimensional space that possesses a conformal field theory (described by a quantum gauge theory).
