From Halopedia, the Halo wiki

This article contains information about a non-canonical subject that, while official, is not part of the established Halo universe.

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.[1] The Pillar of Autumn's original hull classification symbol, SCS, presumably stood for SolCore Ship.[2]

Strangely, one of Halo Infinite's weapons, the CQS48 Bulldog, features a SolCore emblem on top of the gun.[3]