Adrenaline Rush is a rogue ability learned at level 40 for those with the Combat specialization. It instantly increases energy regeneration rate by 100%, effectively enabling the user to use energy-heavy abilities almost without pause, and also boosts melee attack speed.
In raid situations, try to save up your adrenaline rush if you're close to fighting a boss. Adrenaline Rush and [Blade Flurry] are incredible tools for improving burst DPS. Remember to let the tank get some threat before using this, as this can easily lead to overaggroing.
When soloing, try to use Adrenaline Rush early on in fights — you have a much better chance to keep your target stunned and make full use of buffs at the beginning of a fight than at the conclusion. Using AR along with Blade Flurry with [Evasion] and one's favorite damage moves allows rogues to survive multiple-opponent fights that would otherwise necessitate vanishing or using sprint to retreat.
Patch 3.1.0 (14-Apr-2009): Cooldown reduced to 3 min. Was 5 min.