What is "pyrosulfuric acid"

alt. (context inorganic compound English) The acid, H₂S₂O₇, formed by the reaction of sulfur trioxide with sulfuric acid; used in the manufacture of explosives etc. n. (context inorganic compound English) The acid, H₂S₂O₇, formed by the reaction of sulfur trioxide with sulfuric acid; used in the manufacture of explosives etc.