Shout

Shouts are a type of skill that give an enchancement to a group of people. Shouts like "For great justice!" allows adrenaline skills to charge twice as fast, while Charge! allows each person to move faster for a short duration.

You may only have one shout activated at any one time. However if other players are also using shouts, the shout bonuses stack (if the bonus is shared).

As a completely unrelated sidenote, many of the shouts in Guild Wars are references to Geek Pop Culture.
 * "Shields Up!": Star Trek, Star Wars, Most Space Action movies/books.
 * "To the Limit!": Homestarrunner.com's video Everybody to the Limit! (Come on Fhqwhgads)
 * "For great justice!": The badly translated game Zero Wing, and the All Your Base flash video that it spawned.
 * "I Will Survive!": The song of the same title, by Gloria Gaynor.
 * Otyugh's Cry: A fairly popular Dungeons and Dragons monster, called an Otyugh.