Sheet Lightning : A white flash that appears to cover a wide expanse of sky. It is actually the reflection of a lightning flash that is hidden by clouds
Masters of Disaster, Lightning Glossary, The American National Red Cross (and Arizona State University), Washington, DC, USA 2007. http://www.azpbs.org/mastersofdisaster/pdf/Lightni ng/LightningGlossary.pdf, (Lghtng Sfty - Amer) {865}