A NOVA is a type of stellar explosion caused by the collapse of a white dwarf star. It is an extremely bright event that can briefly outshine an entire galaxy. The term 'NOVA' comes from the Latin word for 'NEW' because it appears as a NEW star in the sky. During a NOVA, the white dwarf star releases a large amount of energy, causing its outer layers to be expelled into space. This results in a dramatic increase in brightness, followed by a gradual decrease over several weeks or months.