Positive working print from negative for editorial use — takes wear during handling, preserves the original. Final cut print made only after lock.
You need a working copy of your material as soon as the first development comes back from the lab — that's the dup (dupe). It's created directly from the original negative and gives you a positive working print to work with in the edit, without endangering the expensive original. Every time the editor pulls the reels through the editing tables, when reels are spliced together, when material runs through the synchronizer — the original stays safe. The dup takes the wear and tear, the scratches, the glue spots.
In the classic workflow — and this is still standard for 35mm and 16mm — you send your developed negative back to the lab and have one or more dupes made. The quality of this copy is crucial: it determines how reliably your editor can work, how precisely the edit marks are visible, whether color casts will bother you later. Some DoPs insist on two dupes — one for cutting, one as a backup working copy. This costs money, but saves you nerves if the first dup is damaged or material is lost.
The dup is fundamentally a generational product — it's not the original, sharpness and density can suffer minimally, especially with color materials. This is acceptable because it's not used for finalization. Once the edit is locked and approved, the dup is not used to create the final film — the editor then works with the editing decisions back to the original negative. The original is conformed according to this edit list, meaning: cut or digitally reconstructed. From this original, the final answer print negative is then created for the master copies and the theatrical print.
With digitized material, this process is virtual: you have digital proxies for the editing workflow, the original is safely stored in an archive or on LTO tapes. However, the principle remains the same — you don't work directly with the original. With classic film, however, the dup is indispensable: it's the practical buffer between the valuable original negative and the daily handling in the cutting room.