Image via WikipediaRetcon (v.) - Short for "retroactive continuity," it is the geek-slang term for the rewriting of backstory or fictional history to accommodate a new chapter in an ongoing franchise. This is a pretty common practice in comic books (and, quite frankly, soap operas) where characters are revealed to have very different pasts than previously assumed. For example, at various points Spider-man was said to have received his powers from either a radioactive spider-bite, because he was a totem warrior of a spider-god, or because he was a clone of the original Spider-man. (Currently, I think we've doubled back to option 1, radioactive spider-bite, but don't quote me.) Of late, George Lucas has cornered the market on cinematic retcons with all his Star Wars prequel nonsense rewriting Jedi history.
I bring it up because: The summer movie season has a lot of retcons going for it, either from Wolverine's rewriting of X-men movie history to Terminator: Salvation's resetting the date of Judgement Day--again--and ignoring pretty much everything that happened in The Sarah Connor Chronicles (which was just cancelled). Retcons should not be confused with reboots, which is when a franchise just chucks everything and starts over, much like Batman Begins basically ignored the Tim Burton/Joel Schumacher lineage of batfilms. Thankfully.