Enthalpy - A thermodynamic variable that is a system's internal energy plus the product of its pressure and volume: H = E + PV.
[Chemistry - The Molecular Nature of Matter and Change; Silberberg, Martin; Ed. James M. Smith; p. 228; 1996; Mosby-Year Book, Inc.; St. Louis, Missouri.]
[Oil & Gas Journal; v93; 62-63; 1995.] 
Atmospheric Chemistry Glossary