some definitions of ideology

a) the process of production of meaning, signs & value in social life;
b) a body of ideas characteristic of a particular social group or class;
c) ideas which help to legitimate a dominant political power;
d) false ideas which help to legitimate a dominant political power;
e) systematically distorted communication;
f) that which offers a position of a subject;
g) forms of thought motivated by social interests;
h) identity thinking;
i) socially necessary illusion;
j) the conjuncture of discource and power;
k) the medium in whcih conscious social actors make snes of the world;
l) action-oriented sets of beliefs;
m) the confusion of linguistic and phenomenal reality;
n) semiotic closure;
o) the indispensable medium in which individuals live out their relations to a social structure;
p) the process whereby social life is converted to a natural reality.
from: Ideology an introduction by Terry Eagleton