... and while it's not an adverse action, like probation is, it does mean that the next time the program is up for review a decision will have to be made re: giving full accreditation or closing the program, to my understanding.
Programs end up getting provisional accreditation when they're new or sometimes when 2 programs merge and it changes them significantly. You can get extended for another term once, hence continued provisional accreditation, but not more than that. By then the ACGME either expects the program to be ready for full accreditation or I guess it gets shut down if the ACGME criteria aren't met.