A trust you set up to benefit your spouse after you pass away. Generally, some or all of the assets in the trust are available to your spouse after you pass away and whatever assets remain after your spouse passes away will go to beneficiaries that you name.
For example, if you want your spouse to be able to live in your home when you pass away, but you want the home to go to your children after your spouse passes away, you can leave your home in a trust for your spouse's lifetime and name your children to receive the home after your spouse passes away.