Unix is a trademark, and a concept (of a type of operating system).

Linux is called a "Unix-like" operating system because it doesn't want to upset the trademark holder by inappropriately calling itself Unix (Linux needs to pass the tests to be formally approved as a Unix system) but it's close enough to the concept for us to call it "*nix".

I think the other respondent mean 'proprietary' (not 'property')!

Unix is property software and Linux is open source they are similar and if you are familiar with Unix, you can learn Linux.