The word "core" refers to the center or central part of something. It can describe the most important or essential part of a subject or an object. Full definition
There will have to be a common core of work, of course, but opportunities must be provided and requirements formulated so as to allow and to foster necessary and fruitful specialization. (religion-online.org)
Should there be a common core of knowledge that all people getting degrees in education are required to know and be able to do? (gse.harvard.edu)
The smartphone is well equipped with dual core processor of 1.5 GHz, 16 GB memory and 2 GB RAM. (newgadget.org)