For the EU passports holders there are two types of
NIE. You can get a NIE «number» or a NIE «card»:
A NIE number is just a number assigned for
administrative purposes: purchase property, investment,
tax payment
A NIE card is a little green card also referred to as a
residency certificate or residency card for life in Spain. This residency certificate is equivalent to a NIF — the ID card for Spanish citizens