Is IIS a windows application or a windows service?

Question

Recently this question was asked to me in an interview.

 

I reasoned since we do not use any browser to open IIS, it cannot be Web Application

and since window services do not have a UI, but IIS has one, IIS cannot be windows service,

hence it should be a windows application.

 

I was not able to find anything on internet about this. What is the right answer, please let me know.