Berserk means wildly out of control, filled with violent rage or fury. When someone goes berserk, they lose all sense of calm and reason, acting with explosive anger or chaos.

The word comes from legendary Norse warriors called berserkers who fought with such fierce, reckless fury that they seemed almost superhuman. These ancient fighters would charge into battle without armor, seemingly feeling no pain, terrifying their enemies with their wild ferocity.

Today we use berserk more broadly. A crowd might go berserk with excitement at a concert. Your normally calm teacher might go berserk when the class erupts into a paper airplane war. A squirrel discovering that another squirrel raided its acorn stash might go absolutely berserk, chattering and racing around in furious circles.

The word suggests a complete loss of control: anger so extreme it becomes unhinged and wild. Someone who gets frustrated or upset isn't necessarily berserk, but someone who starts screaming, throwing things, and acting completely wild has gone berserk.