NIE - Paper Document Versus a Plastic Card

@Eduardopiriz

The NIE (Numero de Identidad) is your unique tax identification number. The TIE (Tarjeta de Identidad) is a biometric residence permit for non-EU citizens (and includes your NIE on it). You can get a NIE independent of any visa/residence application, and this would be necessary if you want to buy a property in Spain. Residence applications are typically 2 stages: the appropriate residence visa at your local Spanish embassy (e.g. No Lucrativa Visa or Digital Nomad Visa), followed by the TIE application once you arrive in Spain.

Pedantically, the number on your Australian passport cannot be a NIE, as that's a Spanish thinggy. :-) I don't know what an Australian tax number is called (TFN, right?). I also know zip about Australian passports, so if you say it has your tax ID number, I'll take your word for it. But most passports have a passport number, but do NOT include your tax ID / social security number - my UK passport certainly doesn't!