Mason and Dixon Line also called Mason-Dixon Line, originally the boundary between Maryland and Pennsylvania in the United States. In the pre Civil War period it was regarded, together with the Ohio River as the dividing line between slave states south of it and free-soil states north of it.
The term Mason and Dixon Line was first used in
congressional debates leading to the Missouri Compromise (1820).
Today the Mason and Dixon Line still serves figuratively as the political and social dividing line between the North and the South, although it does not extend west of the Ohio Rive