A spread is a predefined strategy constructed from payer and receiver swaptions.
With a spread you can do either of the following:
Buy a receiver swaption and sell a receiver swaption with the same expiry but different strike prices and notionals.
Buy a payer swaption and sell a payer swaption with the same expiry but different strike prices and notionals.
For more information on a swaption (and how to price it and what points to consider) see Swaption.
Advantages of a Swaption Spread Strategy
In a swaption spread strategy, the cost of one of the options reduces or cancels the cost of the other.