de·mar·ca·tion / ˌdēmärˈkāshən/ • n. the action of fixing the boundary or limits of something: the demarcation of the maritime border. ∎  a dividing line.DERIVATIVES: de·mar·ca·tor / diˈmärˌkātər/ n.

demarcation marking a boundary, orig. applied in the phr. line of demarcation to the division of the New World in XV between the Spaniards and the Portuguese. XVIII. — Sp. demarcación, f. demarcar mark out the bounds of, f. de- DE- 3 + marcar MARK; see -ATION.
Hence demarcate vb. XIX.

demarcation (dee-mar-kay-shŏn) n. the marking of a limit or boundary. line of d. a red or black line marking the boundary between necrotic and healthy tissue in gangrene.