Mason-Dix ‧ on Line, the /ˌmeɪs ə n ˈdɪks ə n laɪn/ BrE AmE
the border between the states of Maryland and Pennsylvania in the US. It is known for dividing the states of the South where it was legal to own ↑ slave s from the states of the North where it was illegal, until the end of the American Civil War. Some people still consider it to be a dividing line between the North and South of the US.