1. the body of doctrine, myth, belief, etc., that guides an individual, social movement, institution, class, or large group.
2. such a body of doctrine, myth, etc., with reference to some political and social plan, as that of fascism, along with the devices for putting it into operation.
3. in philosophy, the study of the nature and origin of ideas.a system that derives ideas exclusively from sensation.
4. theorizing of a visionary or impractical nature.
(Random House Unabridged Dictionary)
In Ideology: An Introduction, Terry Eagleton describes ideology as follows:
A dominant power may legitimate itself promoting beliefs and values congenial to it; naturalizing and universalizing such beliefs so as to render them self-evident and apparently inevitable; denigrating ideas which might challenge it; excluding rival forms of thought, perhaps by some unspoken but systematic logic; and obscuring social reality in ways convenient to itself. Such `mystification', as it is commonly known, frequently takes the form of masking or suppressing social conflicts, from which arises the conception of ideology as an imaginary resolution of real contradictions. (5-6)