Diagonal Spread

What Does Diagonal Spread Mean?
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.

Investopedia explains Diagonal Spread
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.