1. The essential part of a seed; all that is within the seed walls; the edible substance contained in the shell of a nut; hence, anything included in a shell, husk, or integument; as, the kernel of a nut. Also a single seed or grain; as, a kernel of corn.
2. The essential part of an operating system. The kernel is generally responsible for resource allocation, low-level hardware interfaces, security, and so forth. Some operating systems have a great deal of functionality implemented in the kernel, a monolithic kernel; others have a microkernel which implements only a bare minimum, with the remaining features require small modules which can be flexibly configured. A monolithic kernel is much faster than a microkernel, though a microkernel can dynamically load and unload modules as needed to reduce resource usage. The Linux kernel is a good example of an open-source operating monolithic system kernel, the Windows NT kernel is an example of a more layered closed-source kernel design.