ep·ic
   /ˈɛpɪk/
–adjective Also, ep·i·cal.
1.
noting or pertaining to a long poetic composition, usually centered upon a hero, in which a series of great achievements or events is narrated in elevated style: Homer's Iliad is an epic poem.
2.
resembling or suggesting such poetry: an epic novel on the founding of the country.
3.
heroic; majestic; impressively great: the epic events of the war.
4.
of unusually great size or extent: a crime wave of epic proportions.
Let's see... Wolverine's selflessness at the end of X-Men seems heroically epic, considering that he could have flown well over the torch and might have not survived transferring his power to Rogue, Jean's self-sacrifice at the end of X2 was also epic in the heroic sense (for reasons that should be apparent), and the final battle between Magneto's forces, the X-Men, and the human military was surely epic in the size and scale of it (as most superheroic battles, even those involving teams, are typically very small and intimate in scale).
This scene also seems to be going with the fourth definition, but it's certainly not the first "epic battle" in the franchise.
