It's the Agenzia delle Entrate's central database of every taxpayer in Italy, indexed by codice fiscale. It links your income, contracts, real estate, bank movements, and other fiscal data behind the scenes.
It's why your 730 precompilato can be filled in automatically and why the tax office can spot inconsistencies in your declared income. You won't interact with it directly, but it underpins almost every tax process.
Official source
Agenzia delle Entrate
Thanks, we'll take a look.
If you left an email, we'll reply when there's something to say.