Polite people call it "berserker rage"
(Self): Attack Power (lvl 1/2/3) +15/+25/+35, Speed +15/+20/+25
A strong ability for when doing lots of damage is needed. The speed boost allows the slower heroes to quickly get to a battle and still have some time to deal damage properly. Its combination with some of the highest AP heroes can be especially helpful during the early game when most heroes can take very little enemies at a time.