From MEPIS Documentation Wiki
The /boot directory is one of the main subdirectories under / and it contains the files that Linux needs to boot. The Linux kernel (the core of the Linux operating system) is kept in the /boot directory.
When the system boots, it faces a chicken-and-egg situation: accessing the kernel and related files will require an understanding of Linux filesystem layouts - but the kernel and filesystem drivers have to be loaded off those very filesystems that the machine BIOS does not understand. more detail