to make sb / sth seem different from other people or things; to separate sth by marking a line between it and sth else
mark sb / sth off (from sb / sth)
to make sb / sth seem different from other people or things
Each of London's districts had a distinct character that marked it off from its neighbours.
mark sth off
to separate sth by marking a line between it and sth else
The playing area was marked off with a white line.
Definitions from the Oxford Advanced Learner's Dictionary, 9th edition