A plain-English untangling of the number, the green sheet and the residence card for life in Alicante.
The NIE is the number, plain and simple. EU citizens are handed a green certificate, while everyone from outside the EU receives a TIE card — and all three end up being called "the NIE" in conversation, which is where the confusion creeps in.
If you are arriving in Alicante from outside the EU and settling for the long term, the document you will eventually hold is a TIE card showing your NIE number.