Source: The Collaborative International Dictionary of English v.0.48
grand unified theory \grand unified theory\, grand unification
theory \grand unification theory\n. (Theoretical physics)
Any of a class of physics theories that attempts to explain
the electroweak forces, stong force, and gravitation within a
single mathematical conceptual scheme. In the 1990's stringtheory and superstring theory were prominent examples.
Abbreviated GUT, plural GUTs.
[PJC]