As the others made a good point, Linux is the kernel (program that connects hardware altogether and manages processes). GNU is an organisation beginning in 1983 that made some vital userland programs (Bash, GCC, readline, GNOME, GTK, GIMP, etc.) as a replacement of the proprietary ones found in UNIX and Windows. Linux is created by a Finnish student Linus Torvalds and is not a part of the GNU project but it's been licensed under the GNU General Public License (GPL), the first free software license.

Linux is used by a lot of companies, and some of the products that have Linux inside refuse to accept the paradigm of software freedom. Examples of this are: Chrome OS, Windows Subsystem for Linux, Google Android and some (but not all) appliances (like routers) that are locked-in and contain proprietary blobs.

Therefore, in technical discussions, I use the word "Linux" to refer to the OS, as "this software is compatible with Linux". But, when I want to stress out software freedom, given a large influence of the GNU project, I say "GNU/Linux".

For me its GNU/linux formally. Linux would not mean anything to me without the gpl. I would likely be using freeBSD or sticking with windows/mac. Heck I would be using mac now if they had not abandoned their great warrantly support of pre 2010

It depends on what matter to you. I use a GNU/Linux distribution and I call it that such because I think the project deserves to be better known. I say FLOSS rather than FOSS because I value freedom.

tl;dr - people can be silly.

The goes very in-depth on every question you might have on why to call it GNU/Linux. Whether that makes you more or less likely to actually call it that is up to you!

They’re both so good, I can’t choose.

i am sry to say but half my friends dont know what linux is except android runs on it they are surprised that linux can run on computers

so ... I just say linux

Also love this picture!

https://youtu.be/vjMZssWMweA?t=1871