[1] From a traditional photographic perspective, an interpositive (short for intermediate positive) is the negative image of the original camera negative, which is an intermediate step towards creating the positive (exhibition) print.
The interpositive historically had only one purpose, namely to be the element which is used to make the internegative.
[contradictory] All lights and opticals from the answer print are repeated when striking the interpositive, and once the IP exists the original negative can be vaulted.
Historically, interpositives were the element of choice for film-to-tape transfers: However, with improvements in resolution and dynamic range for home viewing, scanning the original camera negatives has become preferrable.
Reversal B&W processing can also be achieved from an interpositive by means of various kits and published recipes.