What does "Core" mean in the Context of Library Design?

Question

I often see other developers naming libraries with "CORE". What does it actually mean?

Answer 1

In my opinion, CORE means something indispensable. Math functions and other functions with utility purposes are not in the core. They are rather "Utils".

The core is that part that makes everything else exist - without it, the others make no sense. Other stuff, that is not in the core can (not always possible by design) to be removed.