Definition
Backdoor triggers are input patterns that make a model switch to a hidden, attacker-chosen behavior, while it behaves normally on all other inputs. In subliminal-learning experiments, a trigger-conditioned behavior (for example, replying in French only when a particular name appears) was passed to a student through number sequences containing neither the name nor any French. This shows that a backdoor can propagate through distillation without the trigger or its effect being visible in the training data, which makes it much harder to detect by inspecting the data.