What is GNU?
GNU is an operating system and an extensive collection of software that forms part of what people refer to as the GNU plus Linux operating system (or erroneously just Linux).Richard Stallman announced the GNU project in 1983. The operating system was to be a free software replacement to the proprietary UNIX operating system.
In 1992 the GNU operating system almost had the entirety of its components created, however one critical part was missing, the kernel.
What is Linux?
Linux is a kernel and is not an operating system unto itself, instead is a critical component in the GNU plus Linux operating system.Linus Torvalds began development on the Linux kernel in 1991 after frustrations relating to the MINIX licensing at the time. The Linux kernel was originally licensed to prohibit commercial redistribution.
In 1992 Linus liberated his kernel relicensing it under the GNU GPL. Now under a free licence and considered free software, the Linux kernel and GNU operating system, along with it's extensive collection of software can pair in a mutually beneficial relationship.