It is based on a comic book series of the same name. 
The "X-Men" are people who have undergone the next phase of evolution, each possessing a unique newly acquired ability.
The X-Men series follows their stories, with two sides of X-Men often battling each other over their worldview—one team of mutants who want to coexist peacefully with humans—the other who believe that humans and mutants should never coexist.
X-Men mainly uses fantasy elements relating to transhumanism, the X-Men themselves and their enhanced abilities link closely to humans who want to be better than themselves. They are somewhat transhuman in their own right.