EUR1 Certificate is a certificate based upon treaties between EU and third countries; giving reduced customs duties when importing to EU. To obtain this kind of certificate for a specific shipment the producer or shipper must be able to prove the origin of the goods. He can do it by providing a valid Certificate of Origin; therefore certifying the full and true origin of the goods to be the country of which the EUR1 Certificate is for.
Note that this is not by automatic the same as duty-free import to EU; the level of customs duty fee reduction also depends on the specific agreement between the country of origin and EU. The treaties regulation the EUR1 are named GSP – Generalized System of Preferences.