What is a core company?

Excuse me, could you please clarify what you mean by "core company"? Is it referring to a company that serves as the backbone or central entity within a larger organization or industry? Or does it signify a company that possesses a strong competitive advantage and holds a pivotal role in its market niche? Additionally, I'm curious to know if there are any specific characteristics or attributes that typically define a core company, and how one might go about identifying such a company within a given industry or sector. Your insights would be greatly appreciated.