Asked by Alan Stark
Lightning is a beautiful yet dangerous natural phenomenon, which is formed in electrically charged storm systems. Exactly how lightning is formed continues to remain a mystery, and a number of different hypotheses exist. Sheet lightning is when we see a luminous white sheet during a thunderstorm. This, however, isn’t a distinct form of lightning. The flash is just hidden by the clouds, making them glow either because it’s really far away or it’s going between the clouds.
Elisa Jones, Science Museum explainer