Volatile content refers to the amount of volatile compounds, such as water, carbon dioxide, and sulfur dioxide, present in a magma. The volatile content is significant in volcanology for understanding the explosivity of volcanic eruptions, the formation of different volcanic rocks, and the degassing processes during magma ascent.
Reference: Wallace, P. J., & Edmonds, M. (2011). “The Sulfur Budget in Magmas: Evidence from Melt Inclusions, Submarine Glasses, and Volcanic Gas Emissions.” Reviews in Mineralogy and Geochemistry, 73(1), 215-246.