Definition
A small number of key people in the organization who persistently resist the transformation and will lead others to resist as well; the principle for handling them is to give them a chance but not wait indefinitely, and to focus main energy on pioneers and the middle group. From a publicly published book, not textbook terminology.
In detail
People in a transformation fall roughly into pioneers, the majority in the middle, and a small number of holdouts. The literature observes that most of the middle shifts as visible results accumulate, and that what truly stalls a transformation is a small number of people in key positions who obstruct it openly or quietly, like antibodies rejecting a transplanted organ. Supporting only the promoters while avoiding the antibodies is a common cause of stalled transformations; the way to handle them is to communicate first and then adjust roles, not to push them out from the start.
Example in practice
A workshop supervisor repeatedly told the team that "Kaizen weeks are a campaign and will pass soon," and leftover items from two Kaizen weeks went unexecuted. The value stream leader spoke with him privately and asked him to lead the next Kaizen week; two months later he still refused to cooperate, so the general manager reassigned his position, and the closure rate of leftover items rose accordingly.