In options and futures trading, the purchase of one contract and the sale of another contract that differs from the first only by its delivery or expiration date. An example of calendar spread would be the purchase of a December call with a strike price of $20 and the sale of a June call with the same strike price. An investor would use a calendar spread in order to profit from a change in the price difference as the securities move closer to maturity. Also called horizontal spread, time spread.