Platform Independence-> Means that your code can run on any platform be it is Windows,Linux,Unix etc in the same manner
Explanation-> .Net is Platform Independent yet it is platform dependent,
Why-> .Net Application is compiled into msil and .Net needs CLR to be installed on the platform to run that msil,so if you have msil code you can run it on any platform which have clr installed but if you do not have clr installed you cannot run msil code and clr is build keeping in mind to be run only on windows and you cannot install clr on Linux Platform that is why you need Windows Server to run .Net applications because they have CLR installed.
Hope i am able to clarify your doubts.