The Collaborative International Dictionary of English v.0.48:

Demarcation \De`mar*ca"tion\, n. [F. d['e]marcation; pref.
   d['e]- (L. de) + marquer to mark, of German origin. See
   Mark.]
   The act of marking, or of ascertaining and setting a limit;
   separation; distinction.
   [1913 Webster]

         The speculative line of demarcation, where obedience
         ought to end and resistance must begin, is faint,
         obscure, and not easily definable.       --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

demarcation
    n 1: the boundary of a specific area [syn: limit,
         demarcation, demarcation line]
    2: a conceptual separation or distinction; "there is a narrow
       line between sanity and insanity" [syn: line, dividing
       line, demarcation, contrast]