Regex = REGular EXpression.
http://en.wikipedia.org/wiki/Regular_expression
Also known as "the stuff that Yahoo, Google and other search engines do their best to ignore in order to maximize profits from sponsored hits and prevent the users from finding what they're looking for". ;P
If I had the $$$ to do it, I'd start a web search engine called lookstupid.com Why that? "Look, you stupid computer! Stop trying to out-think me and just search for EXACTLY what I entered!"
Search engines used to obey things like "quoted strings", where only hits were returned if the page contained EXACTLY what was between the quotes. Boolean operators like AND, NOT, NEAR were obeyed. These days they're typically completely ignored.
lookstupid.com would strictly obey them. I'd even have an IN-ORDER operator so if you know some of the words, perhaps from a book title or song lyric, but not the exact and complete thing, you could enter what you know with IN-ORDER and only hits with those words in that order, first to last, would be returned.
Search engine programmers all need tied to a chair and made to read a few dozen books on this stuff. :P