The term "ideology" was originally coined around the time of the French Revolution to refer to the study of ideas. However, Marx and Engels gave it a negative connotation, seeing ideologies as illusions used by the ruling class to maintain power.

In the 20th century, theorists like Mannheim, Gramsci, and Althusser helped rehabilitate the concept of ideology. They saw ideologies as an inevitable product of social conditions, exercising cultural power through institutions beyond just the state. This view opened up ideology as a valid object of study.

Ideologies are systems of political thought and belief held by significant social groups. They compete to shape public policy and justify or contest political arrangements. Common ideologies include nationalism, liberalism, conservatism, socialism, communism, and fascism. Ideologies order social reality through symbolic "maps" of concepts like liberty, authority, rights, etc. They also organize social and historical time into political narratives.

The meanings of ideological concepts are stabilized within each ideology through linking concepts in certain patterns and prioritizing some over others. This gives ideologies their internal structure. Ideologies have permeable boundaries and "family resemblances" rather than being fixed monoliths. They are flexible ways of packaging political concepts that adapt over time.

Discourse theory sees ideologies as frameworks of communication and symbols that shape identity. Post-Marxists view them as necessary illusions that temporarily cover up social antagonisms. 

In addition to texts, ideologies appear in visual imagery, metaphor, and appeal to emotions. They mobilize support beyond just rational argument. Contemporary ideological fragmentation coexists with the persistence of broad traditions like liberalism and conservatism that still influence politics.

The study of ideologies remains focused on actual political thought and discourse. Their flexibility and ubiquity make them indispensable resources for understanding politics.