«إجماع من بعدهم فيما لم يوجد فيه قول السلف»
Consensus of those after the Companions concerning a matter for which no view of the early predecessors is found.
«من بعدهم» refers to subsequent qualified jurists. «لم يوجد فيه قول السلف» means that no earlier Salaf position is known on that issue.
One can imagine a new legal problem without a recorded earlier opinion on which later mujtahids agree. That scenario illustrates the definition; it is not being asserted as an actual, documented historical consensus.