Anti-Corruption Layer
also called ACL
A translation layer that converts a legacy or external system's model into your own, so its concepts do not leak into your domain.
Legacy systems carry models shaped by decisions made decades ago, and integrating with one naively imports those decisions permanently — the seven-character customer code, the status field with fourteen values of which four are used, the concepts that exist because of a 1998 reorganisation.
An anti-corruption layer sits at the boundary and translates in both directions. Inside it, the mess. Outside it, your model.
It is one of the few pieces of deliberate indirection that consistently earns its cost, because it means the eventual replacement of the legacy system is a change to one component rather than to everything that ever touched it.