Etymology

First recorded c.1752, from linea de demarcacion and/or linha de demarcaçao, the demarcation line laid down by the Pope on May 4, 1493, dividing the New World between Spain and Portugal on a line 100 leagues west of the Cape Verde Islands. Both derive from a verb demarcar, itself from de- + marcar 'to mark' (itself from marcare, from the Germanic root of march)

Noun

1. The act of marking off a boundary or setting a limit, notably by belligerents signing a treaty or ceasefire.
2. A limit thus fixed, in full demarcation line.
3. Any strictly defined separation

   There is an alledged, in fact somewhat artificial demarcation in the type of work done by members of different trade unions.