Linux, the kernel developed and distributed by Linus Torvalds et al, contains non-Free Software, i.e., software that does not respect your essential freedoms, and it induces you to install additional non-Free Software that it doesn't contain. Even after allegedly moving all firmware to a separate project as of release 4.14, Linux so-called "sources" published by Mr Torvalds still contain non-Free firmware disguised as source code.
Free Software Foundation Latin America (FSFLA) joined the (then non-GNU) Linux-libre project as part of its campaign dubbed "¡Sé Libre!", to encourage and enable users to go beyond using some Free Software, and rather seek and choose freedom.
GNU Linux-libre is a project to maintain and publish 100% Free distributions of Linux, suitable for use in Free System Distributions, removing software that is included without source code, with obfuscated or obscured source code, under non-Free Software licenses, that do not permit you to change the software so that it does what you wish, and that induces or requires you to install additional pieces of non-Free Software.
A Linux-based system is a modular Unix-like operating system, deriving much of its basic design from principles established in Unix during the 1970s and 1980s. Such a system uses a monolithic kernel, the Linux kernel, which handles process control, networking, access to the peripherals, and file systems. Device drivers are either integrated directly with the kernel, or added as modules that are loaded while the system is running.