what IIS server?why using IIS sever in asp.net?

http://www.iis.net/learn/get-started/whats-new-in-iis-8/iis-80-using-aspnet-35-and-aspnet-45, http://www.asp.net/web-forms/tutorials/deployment/deploying-web-site-projects/core-differences-between-iis-and-the-asp-net-development-server-cs, http://www.codeproject.com/Articles/42724/Beginner-s-Guide-Exploring-IIS-6-0-With-ASP-NET, http://en.wikipedia.org/wiki/Internet_Information_Services, http://www.dotnetfunda.com/articles/article1247-how-to-host-aspnet-application-on-the-web-server-iis.aspx