It means every marketing asset — ad accounts, analytics, domain, website, email lists, business profiles, creative — lives in accounts registered to your business, where firing any vendor costs you nothing but their labor.
The opposite is renting: the agency's ad account, the developer's hosting, the freelancer's stock-photo licenses. Renting feels identical until the relationship ends — then the meter shows.
The test is exit-cost: list every marketing asset and ask what leaves if each vendor does. Anything that walks out with them is theirs, whatever the invoices said. (This is our founding doctrine, and the audit takes fifteen minutes.)