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.
GNU Linux-libre is a project to maintain and publish 100% Free kernel forked from 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.
For example , Linux contains RTL8723BS WiFi driver , realtek HD audio driver and so on