It denotes a possible future theory that might explain gravity and electromagnetism simultaneously.
It is a label given to postulated models that simultaneously might explain electromagnetism, the weak force, and the strong nuclear force.
It means that all scientists agree on the interpretation and implementation of the details of the theory.
It means a theoretical model that can explain both star formation and supernova explosion.
It means that all forces in nature would be explained by a single all-encompassing theory.