Hegemony is a form of control exercised primarily through a society's superstructure, as opposed to its base or social relations.
Hegemony is leadership to be exercised by the proletariat (revolutionary class) over the other exploited classes.
Hegemony is an exclusion in a perpetual process (and thus incomplete) guaranteed on the one hand by the failure of any particular demand to represent the whole population, and on the other, by the split nature of every subject (and thus the inability to fully incorporate the outside in the inside).
Hegemony is dynamic and does not just passively exist as a form of dominance. It has continually to be renewed, recreated, defended, and modified. It is also continually resisted, limited, altered, challenged by pressures not all its own.
Hegemony is a process, not a system or structure (though it can be schematized as such for the purposes of analysis).
Hegemony is concerned with whole social processes and distributions of power and influence and thus goes beyond culture(in which men define and shape their whole lives) and beyond ideology (in which a system of meanings is a projection of a particular class interest).