grand unified theory

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A theory of elementary forces that attempts to describe the weak, strong, and electromagnetic interactions as low-energy manifestations of a single unified interaction.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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 string theory and superstring theory were prominent examples. Abbreviated GUT, plural GUTs.