Short Box

Sells a box spread, a short call spread and a short put spread on the same two strikes and expiration, a package worth the distance between the strikes at expiration no matter where the underlying finishes.

Traders use it as a financing structure, taking in proceeds now and repaying the strike width later, so the implied rate is what the sheet derives from the four quoted legs. All four contracts are priced from bid and ask, since the entire calculation lives inside the spread. American style options carry early assignment risk that a European settled index box does not.