The latest X-Men adjacent film from Fox is Deadpool 2, and while the film continues its predecessor's tradition of mocking the universe-building prevalent in other superhero movies, it also engages in quite a bit of of super team construction of its own. The film introduces the X-Force, a superhero team that already has its own spinoff movie in the works, but it's quite a bit different from the X-Force in the Deadpool comics that fans already know and love. The film version sees Deadpool put together a team consisting of Domino, Shatterstar, Bedlam, and, uh, Peter, and it's a fun superhero team for sure, but outside of sharing a few members, it doesn't bear a huge resemblance to the X-Force teams of the comics.
There have been many incarnations of X-Force since the first team debuted in 1991, but they can essentially be boiled down to two distinct variations. The first was nothing more than just another X-Men team, more or less. In the '80s and especially in the '90s, the X-Men were by far the most popular comic in Marvel's stable, and as a result the original team received numerous spinoff teams such as Excalibur and X-Factor. The first was the New Mutants, a team made up of younger mutants who were basically X-Men in training — and who also have their own separate movie in the works.
After debuting in 1982 and appearing throughout the decade, the New Mutants popularity waned until 1990 when the character Cable, a time-traveling warrior, was introduced as their new leader and mentor. The team soon underwent an "extreme" '90s redesign, swapping out a few members for new, grittier characters like Domino and Shatterstar and officially becoming X-Force in 1991. This X-Force team, led by Cable and made up mostly of former New Mutants characters, wasn't too different from a standard X-Men team; with the exception of some characters' use of guns and their very '90s attitude (they were totally radical). Their self-titled series sold well, and they were extremely popular in the years following their debut. Eventually, however, they suffered from being a product of their time, and the series was unsuccessfully retooled in 2001 as a bizarre reality star-focused team (it was the early 2000s!) before being canceled the following year.
In 2008, the X-Force name was revived, but as an entirely different team than before. This version was a secret black ops team founded by the X-Men's leader, Cyclops, as a way to deal with threats in ways the X-Men themselves couldn't. Basically, he made them so they could secretly kill bad guys. This group was made up of more morally wishy-washy characters, like Wolverine and X-23, while still bringing back a couple of the more ferocious members of the original X-Force, like Domino. It was this version of X-Force that eventually counted Deadpool as a member, though the character had frequently tussled with the original group as well in the '90s.
After a while, Cable returned and formed his own old school X-Force, while the black ops X-Force also continued, meaning that for a short time, there were two X-Forces in operation in the Marvel Comics universe. These two teams eventually became one in 2014 under the simple banner of X-Force, but the new series lasted just 15 issues before being canceled. There hasn't been another X-Force comic since.
Given the many changes over the history of X-Force, different fans will have different ideas of what an X-Force team should look like on film. Some will favor Cable training a group of young mutants to be warriors, while others will prefer a group of hardened assassins going on controversial missions. Deadpool 2 takes elements from both versions to create its own version of X-Force, and Fox is likely to continue to blaze its own path when creating their upcoming X-Force movie.