A piece of music, normally written about a political subject and intended to drive home some message. Will inevitably be Anvilicious, not that there's anything wrong with that. Since they are also used to educate people, unite them in the cause, and should be easy to learn, they are often prime candidates for a rousing Crowd Song or an Audience Participation Song. This sort of music is at least Older Than Steam, and may well be older still. Compare Hail to the Thief, which can sound similar but is used to emphasize setting instead of make a direct political point.