Spanish citizens:
The fiscal code, Número de Identificación Fiscal (NIF) is a form of tax identification in Spain, and is exactly the same as your DNI (identity card).
Non-Spanish citizens:
The fiscal code (NIF) is the same as the Foreigner’s Identification Number (NIE), which is assigned to non-Spanish persons living in Spain. If you don’t have a Número de Identidad de Extranjero (NIE), you can obtain more information by contacting the Spanish National Police.