ISOLINUX is a bootloader used for booting Linux operating systems from ISO 9660 filesystems, commonly found on CD-ROMs and USB drives. It is part of the SYSLINUX project and is designed to be simple and lightweight, making it ideal for creating live CDs or installation media. The primary function of ISOLINUX is to load the Linux kernel and initial RAM disk, allowing users to start their operating system without needing to install it on a hard drive. It supports various features, including boot menus and configuration options, enhancing the user experience during the boot process.