a guess, but it may refer to the median number of programs that applicants ranked, and it shows that for successful matches the number is 8 vs unsuccessful of 3...
Really, I have no idea what it means otherwise (and assuming I looked at the stat you are asking about)....
Edit: I was pretty close - a contiguous rank is determined by the number of programs any individual applicant ranked within one specialty before listing a different specialty, as explained in the same PDF from 2006:
In general, applicants are more likely to be successful if they rank more programs in their de-
sired specialty. To quantify this aspect of applicant behavior, we tallied the number of pro-
grams ranked in the first-choice specialty before a program in another specialty appears in the
applicant's rank order list.
It is quite common for an applicant to include ranks for programs in second- and even third-
choice specialties along with ranks for different programs in the first choice specialty. Usually,
all of the ranks for programs in the preferred specialty precede those for programs in other spe-
cialties, but occasionally an applicant will intersperse ranks for programs in the first-choice spe-
cialty with ranks for programs in other specialties. For example, for those preferring Anesthesi-
ology, 736 applicants ranked only Anesthesiology programs, 207 ranked programs in other spe-
cialties only after ranking all desired Anesthesiology programs, and 71 ranked other programs
interspersed with Anesthesiology programs. These distributions are different for other special-
ties.