The low-level system software is referred to as the Linux kernel. It's used to keep track of resources and give a user interface. The Linux® kernel is the core interface between a computer's hardware and its programmes and is the most important component of a Linux operating system (OS). It communicates between the two, allowing for the most efficient use of resources.
The kernel is so named because it exists within the OS and handles all of the key functions of the hardware, whether it's a phone, laptop, server, or any other type of computer, much like a seed inside a hard shell.
Yes, it is permissible to make changes to the Linux kernel. The GNU General Public License governs the distribution of Linux (General Public License). End users can modify and alter any project released under the GPL.