Ever since Fox signed a deal with Mark Millar to consult on the studio’s superhero films (see "Fox Does Deal With Millar"), it has been evident that the studio is looking for the kind of coordination among its X-Men films that Marvel Studios has managed to pull off with its slate of films, each of which stands alone as a narrative, but also helps to build a shared universe and pave the way for subsequent films.
Deadpool’s origins lie in the X-Men universe, but in the comics the anti-hero created by Rob Liefeld and Fabien Nicieza originally appeared as a villain in New Mutants and X-Force, although since that time the "merc with a mouth" has starred in his own ongoing series and played a variety of roles in the Marvel Universe while maintaining his wisecracking, fourth wall-breaking, foul-mouthed persona.
Now from writer Simon Kinberg, who wrote the script for X-Men: Days of Future Past, comes confirmation that Fox is indeed creating a shared X-Men cinematic universe and that Deadpool, whose eponymous feature film is slated to debut on February 12, 2016 (see "Deadpool Movie Date Set"), will be a major part of that world.  Kinberg told comicbook.com: "There’s definitely a sort of overall plan that we’ve all been talking about for the X-Men universe now, and Deadpool obviously fits into that.  So yeah, I guess I would say it's part of certainly an overall timeline and thought process that goes into these films, some of which is inspired by the comics and some which is inspired by seeing what Marvel’s done with telling a larger tapestry and linking all those movies together, even as they stand independently as well.  The same kind of thought is going to go into these X-Men movies at Fox."
Fox recently revealed that the Deadpool film would sport a "PG-13" rating, which caused some fans to worry that character will be heavily watered-down for his screen debut, though Fox insiders maintain that they have found a way to keep the "merc with a mouth's" personality intact and still gain a "PG-13" rating (see "Will Deadpool Movie Be Censored?").