Osteopaths have a rotating internship (like allopaths had in the past, but which has fallen away) - in order to do an AOA-accredited residency, you need to do the internship ("rotating" because you got into a bunch of services - it's similar to transitional).
"Linked" is if the internship is part of the program (ie, you do the internship and residency in the same place); if it is unlinked, then the residency is like a 2-4 elsewhere.