A swaption collar is a predefined strategy constructed from payer and receiver swaptions.
With a collar you can do either of the following:
Buy a receiver swaption and sell a payer swaption both with the same expiry but different strike prices and notionals.
Sell a receiver swaption and buy a payer swaption both 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 Collar Strategy
A collar protects you from the risk of rising or falling interest rates as relevant while doing so at a lower cost than the equivalent purchase of a single swaption.