The Core Worlds are the centers of Human civilization, industry, and conflict within the volume of the Persean Sector. In the age of the Domain, the Core Worlds were the heart of the Dominion's presence in the Sector, which was in the middle of a massive colonization effort. For over 200 cycles, humanity has been losing its grip on civilization and struggling desperately to hang on to what is left after the Collapse disabled the Gate network that connected the sector with the Domain.
As of the current version, the term "Core Worlds" refers to the 24 systems that lie at the center of the Persean Sector. Those systems are home to the Hegemony, Tri-Tachyon, the Persean League, the Luddic Church, and the Sindrian Diktat. Unlike the rest of the Sector, the Core Worlds' systems are partially hand-crafted and will always have the same names, and similar locations. Depending on the procedural generation (PG) settings, they may have more worlds than the handcrafted ones.
3 of the systems (Duzahk, Penelope's Star, and the Tia-Ta'xet binary) are uninhabited.