bor·der / ˈbôrdər/ • n. 1. a line separating two political or geographical areas, esp. countries: Iraq's northern border with Turkey.2. the edge or boundary of something, or the part near it: the northern border of their distribution area. 3. a band or strip, esp. a decorative one, around the edge of something: put a white border around the picture.• v. [tr.] form an edge along or beside (something): a pool bordered by palm trees. ∎ (of a country or area) be adjacent to (another country or area): regions bordering Azerbaijan. ∎ [intr.] (border on) fig. be close to an extreme condition: Sam arrived in a state of excitement bordering on hysteria. ∎ (usu. be bordered with) provide (something) with a decorative edge: a curving driveway bordered with chrysanthemums.
Border States in the US, states such as Delaware, Maryland, Kentucky, and Missouri, in which slavery was legal, but which did not secede from the Union during the Civil War.