• Botany

• The kernel of a seed is all that is within the outer coat of the seed, as the edible substance contained in the shell of a nut; hence, anything included in a shell, husk, or integument. The term kernel can also mean a single seed or grain, as "a kernel of corn".

• Computing

• The usage of kernel in computing is derived from the botanical meaning, and the kernel/shell dichotomy. The kernel of an operating system is its essential core component, such as the Linux kernel, and the shell is (nowadays, one kind of) application program that surrounds the kernel, presenting an interface to a user.
• A kernel is also a computing trick in Machine Learning.

• Mathematics

Mathematics has its own further disambiguation page for kernel.

• kernel of a function
• kernel (algebra)
• null space (also called the kernel, in linear algebra)
• kernel (category theory)
• stochastic kernel of a stochastic process