A family office is an organization that manages the financial and personal affairs of a wealthy family. A single-family office serves one family and generally requires very substantial assets to justify its cost. A multi-family office serves several families and spreads that overhead across them.
The term is used loosely, which is a problem for the families it is aimed at. It can describe a staffed organization of dozens managing a single family's affairs, or a marketing description applied to a conventional advisory relationship.
The more useful question is not whether a firm calls itself a family office but which specific services it actually delivers: governance, education, philanthropic strategy, tax and estate coordination, risk management, and reporting. Those are answerable; the label is not.
This definition is provided for educational purposes. It is general information, not investment, tax, or legal advice, and it does not account for any individual circumstances.