Beneficial interest, financial interest and conflict of interest are terms that a Notary Public should know.
If a person is named in a document as someone who will receive some sorts of rights, privileges, or financial endowments, the could be said to have beneficial interest. Notaries are prohibited from Notarizing documents that they are named in as this constitutes beneficial interest which represents a conflict of interest. If you are a beneficiary in a document for perhaps a will, trust holdings, etc., then you would have beneficial interest.
Someone who is named in a document to receive financial sums can be said to have financial interest.
Conflict of Interest
If you gain by having a document signed and you are the Notary, that means you have an interest in having the document signed which constitutes a conflict of interest. Notaries need to be impartial in their duties and should not have any conflict of interest.
Notarizing for Family Members
It is discouraged for a Notary to notarize for family members. It might not directly constitute a conflict of interest, but it looks questionable and it is better to have an outsider notarize signatures for family members as they are completely uninvolved (probably).
123notary Glossary — beneficial interest
Investopedia — beneficial interest definition
The 30 point course — beneficial interest
Just say No #3