I'm still amazed by the number of agency types who get in touch, asking me what I do and jumping in with mispronouced words, incorrectly used jargon, and whilst they type and I search on the interweb, things about themselves that they have apparently embelleshed. It's 2016!!!! Time to get good, people!
GNU is the Free Software Foundation's moniker (GNU's Not Unix), and Linux is the kernel of the operating system. Together they are GNU/Linux - GNU license the tools that you can use with the kernel (eg shells).
Tux is the logo of Linux. You might have seen the grown up Tux (below) more than the baby Tux (above):