It's the payment form used to pay almost every tax in Italy: IRPEF, IMU, TARI, INPS contributions, and many more. You can pay it through your bank, your home banking, or via Agenzia delle Entrate online services.
If you owe anything to the tax office, INPS, or your comune, you'll usually pay it through an F24. Mistakes in the codice tributo or year can take ages to fix.
"To pay his quarterly INPS contributions in Caltagirone, Stefan logged into his bank, picked the F24 module, and entered the codici tributo his commercialista had emailed him."
F24 is one form that handles many taxes. The codici tributo are the part that tells the system what you're paying for. Get those wrong and the payment lands in the wrong bucket.
Official source
Agenzia delle Entrate
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