A catastrophe is a disaster. If a wedding reception is disrupted by a fistfight between the bride and her new mother-in-law, you could call the occasion a catastrophe.
Catastrophe comes from a Greek word meaning "overturn." It originally referred to the disastrous finish of a drama, usually a tragedy. The definition was extended to mean "any sudden disaster" in the 1700s. Nowadays, catastrophe can be used to refer to very tragic events as well as more minor ones. A hurricane destroying hundreds of homes is certainly a catastrophe; baking a birthday cake without following a recipe might also result in catastrophe, if you don't know anything about cooking.