A callable bond is a type of bond that allows the issuer of the bond to retain the privilege of redeeming the bond at some point before the bond reaches its date of maturity. Wikipedia

A bond that can be called (redeemed) by the issuer prior to its maturity, on certain call dates, at call prices. On the call dates, the issuer has the right, but not the obligation, to buy back the bonds from the bond holders at the call price. Technically speaking, the bonds are not really bought and held by the issuer, but cancelled immediately or no longer accrue interest at the original coupon rate. Wiktionary