From Traderpedia

Definition: The purchase of one month futures or option contract and the simultaneous sale of a different month.

In futures: The purchase of one delivery month of a given futures contract and simultaneous sale of a different delivery month of the same futures contract.

In options: the purchase of a put or call option and the simultaneous sale of the same type of option with typically the same strike price but a different expiration date.}}

Also called a Horizontal spread or Time spread