In World of Warcraft, is when you call upon your allies to assist you in pwning evil beasties of all sorts.
In real life however, is when you seduce a person, with a come-hither expression and demeanor used to pull the person in so that you can hug, snog, whatever it is you do once you seduce someone.
WoW: "AAHHH! 10 Murlocks are upon me!" *summons reinforcements*
IRL (In Real Life): *bites lip, lowers eyes* "I'm summoning you... is it working?" *winks*