It is a filing that small businesses and startups need to file with the Financial Crimes Enforcement Network (FinCEN) of the U.S. Government. It includes information about the business (where it was incorporated, any “doing business as” names, employer identification number, address) AND information about its owners and those who have substantial control over the business (name, date of birth, citizenship, residential address, and identification number [along with an upload of a government-issued ID]).