Linux most commonly refers to either an open-source UNIX-like kernel, or a family of desktop operating systems based on such kernel. This family is often known as GNU/Linux (which is controversial due to the fact that a small number of distros do not use GNU tools, such as Alpine Linux or Android — in short, GNU is not Linux-exclusive, and Linux is not GNU-exclusive).
Linux is not actually derived from UNIX directly (unlike FreeBSD which is). Rather, it was created as an open-source "clone" in 1991 by Finnish-American programmer Linus Torvalds for use on the i386 architecture. Today, Linux is available on practically every architecture, from the 41-year old i386 (until kernel 7.2, that is) to Apple Silicon.
Linux's mascot is Tux the Penguin, however on e621 you will see a lot more art of Xenia the Fox, a rejected candidate mascot that has become Linux's unofficial mascot for furries. https://en.wikipedia.org/wiki/Linux