Indexing? Are you wanting to know what the difference is between a local file path and an http URL? A file path locates a particular file somewhere on the server machine's storage device (hard drive, CD-ROM, whatever). A URL (strictly, a URI) is a name that identifies a particular resource - which is not necessarily a file. An http URI is one that you would use to request a resource from an http server.
More information on the difference is given by the W3C.
