Kernel

The core of the operating system, managing hardware and processes.

The kernel is the part of Linux that actually talks to hardware: it schedules processes on CPUs, manages memory, drives disks and network cards, and enforces permissions. Everything else: your shell, your editor, your web server: is a user-space program that asks the kernel for these services through system calls.

Strictly speaking, "Linux" is the kernel; a usable system is the kernel plus GNU tools, a package manager and the rest, which is why distributions exist. Check yours with uname -r.

See it in practice

$ uname -r

Prints the running kernel version. After a kernel update, this still shows the OLD version until you reboot: a common source of confusion when patching.

Where you'll meet it