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.
Source 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.