Anti-de Sitter/Conformal Field Theory (AdS/CFT) is a mathematical relationship between two separate descriptions of the same physics. According to AdS/CFT, a string theory in a region of Anti-de Sitter (AdS) space is equivalent to a conformal field theory (CFT) on the boundary of that region. Anti-de Sitter space has negative curvature (a two-dimensional plane is curved in a saddle shape rather than flat), and is one of the simplest geometries in which the equations of general relativity can be solved. A conformal field theory is the type of field theory used in the Standard Model. Although AdS/CFT describes an artificially simple situation—we appear to live in flat space, not Anti-de Sitter space—the mathematical correspondence between the two descriptions of physics has allowed relatively straightforward field theory calculations to shed light on problems associated with the quantum mechanics of black holes. AdS/CFT has also been used the other way, with black hole calculations providing insight into complicated particle collisions and condensed matter systems that are difficult to understand with the conventional field theory approach.