O que é Swaption, payer, receiver; callable bond?

A swaption is an option to enter an interest-rate swap at a fixed rate $K$ on a future date. A payer swaption gives the right to pay fixed; a receiver swaption the right to receive fixed. At expiry $T$ a payer is worth $N A(T)\max(S_T - K, 0)$, where $S_T$ is the par rate of the underlying swap then and $A(T)$ its annuity. A callable bond is a bond its issuer may repay early, at a set price on set dates.