A more thorough explanation:

Modified per stirpes is a way of deciding who gets what when someone dies without a will. If the person who died has a surviving spouse, the spouse gets a share of the estate. The rest of the estate is divided among the descendants of the person who died.

In the modified per stirpes system, the estate is divided into primary shares at the generation nearest to the person who died that contains at least one living member. For example, if all of the person's children are dead, but at least one grandchild is alive, the primary shares are determined at the grandchildren generation rather than the children generation.

If a person from the "primary share" generation has died before the person who died, that one primary share is further divided by the number of people at the next generation.

Let's say John dies without a will. He is survived by his wife, Mary, and their two children, Tom and Sarah. Tom has two children, but Sarah has no children.

In this case, Mary would get a share of the estate, and the rest would be divided between Tom and Sarah. However, if Tom had died before John, his share would be divided between his two children.

So, if Tom had died before John, the estate would be divided into three primary shares: one for Mary, one for Sarah, and one for Tom's two children.

Modified per stirpes can get complicated, but it ensures that the estate is divided fairly among the descendants of the person who died.