LATAM context
The number is written in three grouped blocks and ends in a check digit calculated from the ones before it, so a mistyped CUIT gets caught before it's used. The first two digits indicate the type of taxpayer and, for individuals, registered gender. It's the field that ties a bank account to its holder with the tax authority, and it shows up on invoices, contracts and in the header of business bank statements.
Concrete example
A company CUIT looks like 30-71234567-8; an individual's, like 20-12345678-9.
How it shows up on your bank statement
On Argentine statements the account holder's CUIT sits in the header, next to the CBU and company name. It shows up inside transactions when the counterparty included it in the transfer reference, common in business-to-business payments and rare between individuals.
How does finO$ handle this?
finO$ extracts the account holder's CUIT when it appears in the statement header, which lets it automatically group several accounts belonging to the same company even across different banks.