TMZ is reporting that Katherine Jackson, matriarch of the Jackson family, will receive 40% of the Michael Jackson estate. However, she does not get the 40% outright. Rather, the amount is held in trust. The trustees have control of how much is distributed to Kathrine, and upon her death, any remaining funds go to Michael's children.
This actually isn't that uncommon. Although there are many reasons to structure a testamentary dispositon (gift through a will) that way, one obvious reason is to protect those assets from other family members. If Katherine received 40% outright, Katherine would have 100% control over what happens to it, both during her life and after her death. Upon Katherine's death, any remaining amount would be part of her estate and go through intestacy or by the provisions of her will. This could result in family members who were specifically excluded from Michael's will receiving assets through Katherine.
Putting estate assets going to Katherine in a testamentary trust (trust set up through provisions in the will), prevents such an occurrence and helps assure that Michael's wishes as to who exactly benefits from his estate remain intact.
If you have specific wishes as to who, and who cannot, benefit from your estate, a testamentary trust may meet your needs. Contact a licensed attorney who can craft a will and testamentary trust that can help assure your wishes also remain intact.