IIS (Internet Information Services - formerly called Internet Information Server) is a web server created by Microsoft for their operating systems for servers. Its first version was introduced with Windows NT Server version 3.51, and went through several updates. Currently, the most current version is IIS 8.5 (only available in Windows Server 2012 R2 and Windows 8.1)
The version of IIS is tied to the version of the operating system it is running on.
One of its characteristics is to generate dynamic HTML pages, that unlike other web servers, uses proprietary technology, ASP (Active Server Pages), but can also use other technologies with the addition of third-party modules.