Per stirpes Definition
Per stirpes is a Latin phrase (meaning per branch) used in wills that specifies that each branch of the testator's family is to receive an equal share of the estate.
As an example, suppose that the testator is A, whose will specifies that his estate is to be divided among his children per stirpes. A has three children, B, C, and D. B is already dead, but has left two children (grandchildren of A), named B1 and B2. When A's will is executed, under a per stirpes division, C and D each receive one-third of the estate, and B1 and B2 each one sixth, because their "branch" of the family has received one equal share. Under a per capita distribution, each of the surviving descendants B1, B2, C, and D would have received one quarter of the estate.
Similarly, if grandchild B1 had also died before A but left two children, B1a and B1b, a per stirpes division would still give one third to each of C and D and one sixth to B2. The one sixth allocated to the B1 branch would be divided between B1a and B1b, with each receiving one twelfth of the original estate.