If you are a catering operator in Belgium, you may have heard of the term GKS, which stands for Geregistreerd Kassasysteem or Registered Cash Register System. The use of a GKS is mandatory for certain catering operators who exceed a certain threshold of turnover from these services. The use of a registered POS system guarantees that the correct turnover is declared for the calculation of taxes and that the VAT, which the customer pays, is transferred to the Belgian TA.
Source: www.fiscal-requirements.com