A jargon-free look at the NIE number, the green EU certificate and the TIE residence card.
The NIE is the number, and nothing more. EU citizens receive a green certificate; non-EU citizens receive a TIE card. All three are loosely — and confusingly — referred to as "the NIE".
If you are a non-EU national putting down roots in Mallorca for the long term, your destination is a TIE card displaying your NIE number. The green certificate route belongs to EU citizens.