matični broj

1. (of a company or sole trader) registration number; company ID number
   Na fakturi navedite PIB i matični broj firme. — Put the company's tax ID and registration number on the invoice.
   Matični broj piše u rešenju o registraciji. — The registration number is in the registration decision.
2. (of a person) personal identification number; JMBG
   Upišite svoj matični broj sa lične karte. — Enter your personal ID number from your ID card.

Don't confuse it with the PIB (tax ID number): a company has both. The full name of the personal number is "jedinstveni matični broj građana" (JMBG); forms often shorten it to "matični broj".