20 Pa. C.S. § 7502
The following words and phrases when used in this chapter shall have the meanings given to them in this section unless the context clearly indicates otherwise:
"Interested party." Each trustee then serving and each person having an interest in income or principal whom it would be necessary to join as a party in a proceeding for the judicial settlement of a trustee's account. The term "interested party" does not include a person who has not attained majority or is otherwise incapacitated unless a court has appointed a guardian for the person for some purpose other than acting under section 7503 (relating to application of chapter) or an agent has been appointed under a durable power of attorney that is sufficient to grant authority to act under section 7503.
20 Pa.C.S. § 7502