An options strategy established by simultaneously entering into a long and short position in two options of the same type (two call options or two put options) but with different strike prices and expiration dates.

This strategy is called a diagonal spread because it combines a horizontal spread, which represents the difference in expiration dates, with a vertical spread, which represents the difference in strike prices. An example of a diagonal spread is the purchase of a December $20 call option and the sale of an April $25 call.