at the core of a computer’s operating system, that always has complete control over everything.
A full kernel controls all hardware resources (e.g. I/O, memory, cryptography) via device drivers, arbitrates conflicts between processes concerning such resources, and optimizes the use of common resources, such as CPU, cache, file systems, and network sockets. On most systems, the kernel is one of the first programs loaded on startup (after the bootloader). It handles the rest of startup as well as memory, peripherals, and input/output (I/O) requests from software, translating them into data-processing instructions for the central processing unit.
https://en.wikipedia.org/wiki/Kernel_%28operating_system%29
not to be confused with firmware, which is only for low-level devices. kernel, i believe, is used for more complex devices with operating systems.