Answer:
The correct answer is: the amount of heat absorbed or released by a system at constant pressure.
Explanation:
Enthalphy is a thermodynamic property and it is often symobolized with the letter H. It is defined as the amount of energy which can be released in form of heat in a process at constant pressure. The variation of enthalphy, symbolized by ΔH, is the amount of heat released (if ΔH<0) or absorbed (if ΔH>0) during a process at constant pressure, for example a chemical reaction.