What is Eint and when is it present?
More context would be nice. I would guess that it is actually Einit, the initial energy of the system. In intro physics this is either kinetic or potential or both. In thermodynamics it is the initial thermal energy of the system.
You haven't supplied enough information, but best guess is internal energy. Why not post the actual question? We often use internal energy (symbol Eint or sometimes U) to mean the energy of the atoms/molecules in an object due to their thermal motion. For example, if we have an ideal gas, Eint is the kinetic energy of the particles which are moving around randomly. In this example the absoute temperature is proportional to Eint. Double the temperature and you are doubling Eint because the particles are moving faster.
Never heard about "Eint"
RealPro: I would like to know too
I would like to know too :)