What is "linux-libre"

Linux-libre is an operating system kernel and a GNU package that is maintained from modified versions of the Linux kernel. The aim of the project is to remove from the Linux kernel any software that does not include its source code, has its source code obfuscated, or is released under proprietary licenses.

Software components with no available source code are called binary blobs and, as such, are mostly used for proprietary firmware images in the Linux kernel. While generally redistributable, binary blobs do not give the user the freedom to audit, modify or, consequently, redistribute their modified versions.