This is a pretty good definition of ideology.

Ideology is a much-abused word. Many who bandy about this term are under the mistaken notion that ideology is synonymous with strongly holding to philosophical or theological truths. On the contrary, ideology is, instead, an intellectual system of ideas or rigid abstract formulas mixed with scientific jargon and some empirical facts that claims knowledge about reaching perfection in the temporal order.

Catholics should never let themselves be called ideologues. Ideologues attempt, according to Eric Voegelin, “to mold reality into a scheme consistent with a posited or assumed idea.” Proponents are convinced that when the tenets of one’s ideological world-view are properly administered by messianic-elites, society will be transformed into a harmonious secular paradise – in other words, heaven on earth.

From George Marlin at the Catholic Thing