It is a trust developed by a married couple with the purpose of minimizing estate taxes. An A-B trust is a trust that splits into two on the death of the first spouse. It is produced with each spouse putting assets in the trust and naming as the final beneficiary to any appropriate person except the other spouse. The trust obtains its name from the fact that it divides into two upon the first spouse's death - trust A or the survivor's trust, and trust B or the decedent's trust.
The surviving spouse has total control over the survivor's trust, which holds his or her property interests, but has partial control over the assets in the deceased spouse's trust. Though, this restricted control over the assets in the decedent's trust will still allow the surviving spouse to reside in the couple's house and take income from the trust, given that these terms are fixed in the trust. On the casualty of the surviving spouse, the property in the decedent's trust transfers to the beneficiary(s) named in this trust. As this property is not considered part of the second spouse's estate for reasons of estate tax, double-taxation is ignored.