There are two parts to this question. The "What" has been answered many times and is arguably a duplicate

Suggested articles here on unix.SE

• Is Linux a Unix?
• Evolution of Operating systems from Unix

Suggested articles "out there" include

• https://opensource.com/article/18/5/differences-between-linux-and-unix
• https://www.cyberciti.biz/faq/what-is-the-difference-between-linux-and-unix/

Now as to the "Which", one command to use is uname -a. (You can read up on this with man uname.) For example,

• Cygwin - CYGWIN_NT-10.0 MYPC 3.1.4(0.340/5/3) 2020-02-19 08:49 x86_64 Cygwin
• Linux on a Pi - Linux pi 4.9.35-v7+ #1014 SMP Fri Jun 30 14:47:43 BST 2017 armv7l GNU/Linux

There are two parts to this question. The "What" has been answered many times and is arguably a duplicate

Suggested articles here on unix.SE

• Is Linux a Unix?
• Evolution of Operating systems from Unix

Suggested articles "out there" include

• https://opensource.com/article/18/5/differences-between-linux-and-unix
• https://www.cyberciti.biz/faq/what-is-the-difference-between-linux-and-unix/

Now as to the "Which", one command to use is uname -a. (You can read up on this with man uname.) For example,

• Linux on a Pi - Linux pi 4.9.35-v7+ #1014 SMP Fri Jun 30 14:47:43 BST 2017 armv7l GNU/Linux
• Cygwin (not a Linux) - CYGWIN_NT-10.0 MYPC 3.1.4(0.340/5/3) 2020-02-19 08:49 x86_64 Cygwin
• OpenBSD (not a Linux) - OpenBSD localhost.localdomain 6.7 GENERIC#1 amd64
• NetBSD (not a Linux) - NetBSD localhost.localdomain 9.0 NetBSD 9.0 (GENERIC) #0: Fri Feb 14 00:06:28 UTC 2020 [email protected]:/usr/src/sys/arch/amd64/compile/GENERIC amd64
• macOS (not a Linux) - Darwin localhost.localdomain 19.4.0 Darwin Kernel Version 19.4.0: Wed Mar 4 22:28:40 PST 2020; root:xnu-6153.101.6~15/RELEASE_X86_64 x86_64