: Restricts results to URLs containing specified text.
This part of your query suggests you're looking for web pages (index pages, to be specific) that have a certain structure or content. "Index.shtml" implies a webpage, likely a default or main page for a website or a directory, coded in HTML. inurl view index shtml 14 better
In the context of (or Google Hacking), this specific query is a known method for locating network cameras that are broadcasting on the internet without proper authentication. : Restricts results to URLs containing specified text