Inetpub folder related to which server?

Inetpub folder by default,  is the public web root for the built-in Windows Web Server which is related to the installation of MS Internet Information Services (IIS). 

Inetpub folder and sub-folder are part of  the Microsoft Internet Information Services(IIS). It is related to Web Server.

That folder is, by default, the public web root for the built-in Windows web server, called Internet Information Services (IIS). Anything you place on that folder is served by IIS as your web server content pages and downloads.