1. <storage> Main memory or RAM. This term dates from the days of ferrite core memory and, like the technology, is now archaic.
Some derived idioms outlived the hardware: for example, "in core" (meaning paged in), core dump, "core image", "core file". Some varieties of Commonwealth hackish prefer store.
2. <processor> An integrated circuit design, usually for a microprocessor, which includes only the CPU and which is intended to be incorporated on a chiip with other circuits such as cache, memory management unit, I/O ports and timers. The trend in 2009 is to have multiple cores per chip.
The ARM6, ARM7 and ARM8 are early examples, the Intel Core i9 more recent.
3. <language> A varient on kernel as used to describe features built into a language as opposed to those provided by libraries.