General Chemistry Online: Glossary
endothermic
An endothermic process is a process that absorbs heat. A positive sign on heat or on the enthalpy change associated with a process indicates that it is endothermic. Contrast with exothermic.

energy
Energy is a property associated with the capacity to do work.

enthalpy (Symbol: H)
Enthalpy (H) is defined so that changes in enthalpy (DeltaH) are equal to the heat absorbed or released by a process running at constant pressure. While changes in enthalpy can be measured using calorimetry, absolute values of enthalpy usually cannot be determined. Enthalpy is formally defined as H = U + PV, where U is the internal energy, P is the pressure, and V is the volume.

exothermic
An exothermic process is a process that releases heat. A negative sign on heat or on the enthalpy change associated with a process indicates that it is exothermic. Contrast with endothermic.

internal energy (Symbol: U or E)
Internal energy (U) is defined so that changes in internal energy (DeltaU) are equal to the heat absorbed or released by a process running at constant volume. While changes in internal energy can be measured using calorimetry, absolute values of internal energy usually cannot be determined. Changes in internal energy are equal to the heat transferred plus the work done for any process.

thermodynamics
Thermodynamics is the study of energy* transfers and transformations.

work
Work is a process that involves moving an object against an opposing force. Dropping a stone from a window involves no work, because there is no force opposing the motion (unless you consider air friction...). Pushing against a stone wall involves no work, unless the stone wall actually moves.