Tephra is a general term for fragments of volcanic rock and ash ejected during an explosive volcanic eruption. Tephra deposits are significant in volcanology for understanding eruption dynamics, dating geological events, and reconstructing past volcanic activity.
Reference: Thorarinsson, S. (1981). “Tephra Studies and Tephrochronology: A Historical Review with Special Reference to Iceland.” Journal of Quaternary Science, 20(1), 3-21.