Box spread
In options trading, a box spread is a combination of positions that has a certain (i.e. riskless) payoff, considered to be simply "delta neutral interest rate position". For example, a bull spread constructed from calls (e.g. long a 50 call, short a 60 call) combined with a bear spread constructed from puts (e.g. long a 60 put, short a 50 put), has a constant payoff of the difference in exercise prices (e.g. 10). Under the no-arbitrage assumption the net premium paid out to acquire this position should be equal to the present value of the payoff.
They are often called "alligator spreads" because the commissions eat up all your profit due to the large number of trades required for most box spreads.
The box-spread usually combines two pairs of options; and its name derives from the fact that the prices for these options form a rectangular box in two columns of a quotation.
Note that box spreads also form a strategy in futures trading - see below.
Background