Voorlopige Aanslag means a provisional tax decision in the Netherlands. What does this nature of the declaration tell us? It means that it (the Dutch tax authority) has made a provisional assessment of the tax to be paid at a given point in time (the point at which the form is delivered to the taxpayer's hands), which means that it may still change, e.g. a surcharge may be due instead of a refund. The final decision is in turn made by Aanslag.