CORE refers both to a set of instruments, i.e. self-rating questionnaire measures and practitioner completed context setting instruments, collectively “the CORE instruments” but also refers to thinking, particularly about Practice Based Evidence (PBE) in which they were designed so in the entirety “the CORE system”.
There is much more information about the CORE instruments and system at https://www.coresystemtrust.org.uk/.
Mainly chapter 4.
CE was a co-founder of the CORE system and maintains the CORE site.