Demarcation: A setting of limits; a boundary; marking the limits of, delimiting; setting apart, separating. The word "demarcation" is used in medicine mainly in the sense of determining and marking off boundaries. For example, the surface demarcation in respect to damaged tissue can refer to the boundary between the living tissue and the necrotic (dead) tissue.
"Demarcation" descends from the Italian verb "marcare" (to mark). It gave rise to the Spanish "marcar" (to mark) from which came "demarcar" (to fix the boundary of). In 1493, a Spanish noun, "demarcacion," was used to name the then-new meridian dividing the Spanish Indies from the Portuguese Indies. About 1730 English speakers began calling this boundary the "line of demarcation" and, in time, that came to apply to other boundaries.