macOS adopted the Unix kernel and inherited technologies developed between 1985 and 1997 at NeXT, the company that Apple co-founder Steve Jobs created after leaving Apple in 1985. Releases from Mac OS X 10.5 Leopard and thereafter are UNIX 03 certified.

Does Apple use Linux or Unix?

Yes, OS X is UNIX. Apple has submitted OS X for certification (and received it,) every version since 10.5. However, versions prior to 10.5 (as with many ‘UNIX-like’ OSes such as many distributions of Linux,) could probably have passed certification had they applied for it.

Is Mac terminal Unix or Linux?

As you now know from my introductory article, macOS is a flavor of UNIX, similar to Linux. But unlike Linux, macOS does not support virtual terminals by default. Instead, you can use the Terminal app (/Applications/Utilities/Terminal) to obtain a command line terminal and BASH shell.