Mason–Dixon Line

 
Pronunciation: /meɪs(ə)nˈdɪks(ə)n/

noun

  • (in the US) the boundary between Maryland and Pennsylvania, taken as the northern limit of the slave-owning states before the abolition of slavery.

Origin:

named after Charles Mason and Jeremiah Dixon, the 18th-century English astronomers who surveyed it in 1763–7