The word ‘Nerfed’ is used in the game World of Warcraft when the developers see one class (Mage,Warrior, Priest and so on) has an advantage over the other classes, so in the interest of fairness -in the next patch- they reduce the classes power (by reducing attack power, attack cool down times or some other factor) to bring them in-line with the other classes. Gamers refer to this as “LOL!!1! MY CLASS GOT TOTALLY NERFED IN THE LAST UPDATE!1!! LOL!!”
While mildly annoying for most gamers, the nerf is an essential part of the on-line game, if it never happened everyone would be a mage.