Definitions for "grand unified theory"
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 string theory and superstring theory were prominent examples. Abbreviated GUT, plural GUTs.
A theory, not yet developed, that will supposedly describe the strong, weak, and electromagnetic forces as different aspects of a single force. See also: strong force, weak force, electromagnetic force, Theory of Everything, Advanced Topics
Often abbreviated GUT, it is a mathematical theory in which the strong, electromagnetic, and weak forces become aspects of one force. The correct theory has not yet been formulated.