Kernel: The Linux kernel is a Unix-like operating system kernel. It is the namesake of the Linux family of operating systems. Released under the GNU General Public License version 2 (GPLv2) and developed by contributors worldwide, Linux is one of the most prominent examples of free software.
Every time Ubuntu installs a new Linux kernel, the old one is left behind. This means that if you are regularly updating an Ubuntu system the Grub boot menu becomes longer and longer with kernels you don't need anymore.
