Dictionary.net

A faction of the Democratic Party in New York State, so called from an alleged eagerness for radical measures, in allusion to the story of the Dutchman who burned down his barn to clear it from rats. The election of Polk in 1844 resulted in a split of the party in New York into two factions, the "Barnburners," representing the Van Buren wing and opposing the extension of slavery in the territories, and the "Hunkers," representing the administration and its views. In 1848, in the Democratic National Convention there were contesting delegations from New York representing the two factions. Unable to secure complete recognition the Barnburners joined in the Free-Soil Convention, voted for Van Buren, and so helped to elect Taylor. The breach between Barnburners and Hunkers was healed in. 1852, more or less perfectly.