You might call them url shortcodes, shortcuts, abbreviations or otherwise. Firefox calls them keywords. Bookmark a page, edit the bookmark, add a keyword. Now type that keyword into the address bar and hit enter. Boom, it takes you to the bookmarked page.
So instead of typing http://www.scroogle.org/cgi-bin/scraper.htm I can instead just type “search” and boom, I’m there! Props to cryton on freenode#firefox for the info. 🙂