Per stirpes - Latin for 'by the branch' - answers one question every will and trust must face: if a beneficiary dies before you, where does their share go? Per stirpes sends it down their branch of the family, to their children. Arizona's intestate statutes use the same idea under the name 'by representation.'
The alternative, per capita, redivides among the surviving beneficiaries at the same level - the deceased beneficiary's children get nothing. Neither is wrong; they are different intentions, and the two words quietly decide whether a grandchild inherits.
This is a one-line choice in a document that most people never notice until it matters. When you review your will or trust, this clause is worth sixty seconds of attention.
Related reading
Educational information only, not legal advice. Terms have statutory details beyond these summaries - confirm your situation with a licensed professional.