Heat number
The identifier of a batch of metal as poured by the mill, and the key that ties a finished component back to a certified chemistry and set of mechanical properties.
Traceability in fabrication is, in practice, heat traceability: from the mill certificate to the plate, from the plate to the parts cut from it, from those parts to the joints made with them, and from the joints to the component in the dossier.
The chain has to be built forwards, at goods-in. Reconstructing it backwards at handover from delivery notes and memory is the situation everyone is trying to avoid.