Are you sure that "localhost" was part of a URL? Because it's part of the IIS system as well. I found this page via an internet search. It discusses key names and paths, and IIS://Localhost is one of them.
You might be able to find what you need at one of the following IIS links, though:
Integrated Information Systems
IIS Answers - Support Central for IIS 6 and IIS 5
Internet Information Services
IIS Tips, Tricks, and Resources