Main-Core or just Maincore is used to refer to the central elemental or basic characteristic of something or someone. It is strongly related in use to Large-Core and similar
derivatives. It is a portmanteau of Main, which here means the main thing and not a place in USA ---> and Core which is like the kernel or centre of something. (
Apple core is a good reference point here to keep you grounded)
Other close
derivative or strongly related 'Core' word here is Rudecore