1.
If you ~ a piece or length of something, you make it separate, for example by putting a line on it or around it.
He used a rope to ~ the circle...
PHRASAL VERB: V P n (not pron)
2.
If a particular quality or feature marks someone or something off from other people or things, it is unusual and makes them obviously different.
Her clothes, of course, marked her off from a great number of the delegates at the conference...
The traditionalist influences within the navy marked it off as a rather old-fashioned institution.
PHRASAL VERB: V n P from n, V n P as n