depends on your survey if it is depepcited as an area, it may be what was said in the above post.....If it is a line or the words "set off" next to a monument it means that the monument is set off the surveyed property's line by that distance.
For example the language in a deed might read " starting one hundred feet north of an iron round, thence running 300 feet do west...etc." as you can see,,this iron road would not be within the surveyed property so it would be depicted with the words "set off" or Off,, with a distance given.
However without seeing your survey, one is unable to tell if yours is a delineated area of a set off,,or a surveyors note of a "set off" monument.
Bill