GNU/Linux kernel definition

Wikipedia definition

The Linux kernel is a free and open-source, monolithic, Unix-like operating system kernel. The Linux family of operating systems is based on this kernel and deployed on both traditional computer systems such as personal computers and servers, usually in the form of Linux distributions, and on various embedded devices such as routers, wireless access points, PBXes, set-top boxes, FTA receivers, smart TVs, PVRs, and NAS appliances.

While the adoption of the Linux kernel in desktop computer operating system is low, Linux-based operating systems dominate nearly every other segment of computing, from mobile devices to mainframes.

As of November 2017, all of the world’s 500 most powerful supercomputers run Linux.

The Android operating system for tablet computers, smartphones, and smartwatches also uses the Linux kernel.