A more thorough explanation:

Surviving spouse's trust is a type of trust that is controlled by the living spouse in an AB trust scheme. An AB trust is a way for a couple to split their assets into two trusts to limit the estate taxes incurred by their property before being given to the beneficiaries.

The A trust is the surviving spouse's trust, which contains a portion of the assets and allows the surviving spouse some control over the trust. The B trust must be irrevocable, uncontrollable by the surviving spouse, and can only benefit the surviving spouse in limited ways.

For example, John and Jane have an AB trust. John dies, and his assets go into the B trust, which is controlled by the trustee. Jane's assets go into the A trust, which she controls. Jane can use the assets in the A trust for her benefit during her lifetime, but she cannot change the terms of the trust or give the assets to anyone else.

Since the lifetime exclusion amount for estate taxes now is portable between spouses, this system may not benefit as many spouses. However, many still use the AB trust system to limit state estate taxes or to delay all estate taxes.

Overall, a surviving spouse's trust is a way for a couple to protect their assets and limit estate taxes. It allows the surviving spouse to have some control over the trust while still ensuring that the assets are distributed according to the couple's wishes.