kernel

ot noun

1. The core, center, or essence of an object or system. the kernel of an argument
2. The central part of many computer operating systems which manages the system's resources and the communication between hardware and software components. The Linux kernel is open-source.
3. A function used to define an integral transform. The Dirichlet kernel convolved with a function yields its Fourier series approximation.
4. For a given function (especially a linear map between vector spaces), the set of elements in the domain which are mapped to zero; (formally) given f : X → Y, the set {x ∈ X : f(x) = 0}. If a function is continuous then its kernel is a closed set.