v. to dual-wield, dual wielding, dual-wielded; adj. dual-wielded
n., in games, esp. role-playing and FPS computer games, a technique, skill or ability that allows a character to use two weapons at once, one in each hand; may also be permitted by an “ambidextrous” skill. Ex: My dual-wielded SMGs tore the zombies in half! See two-gun mojo.
Addendum: Popularized by Halo 2 and Halo 3; but the term is much older than that; it probably originated in Hong Kong action film fandom.