SolCore

SolCore was the original name for the central human government in the Halo universe, rather than the Unified Earth Government and its United Nations Space Command. By the time it encountered the Covenant, it had colonized seven worlds and discovered four "lost colonies" of humans living on the alien planets. The Pillar of Autumn's original designation, SCS, presumably stands for SolCore Ship.

The word Sol most likely is a reference to the Solar System and the system's medium sized star, Sol. Core most likely means that it is the core government of the Sol System and all its colonies.