If you're asking about "negotiating mandate" here: it's a step in the EU legislative process, which is initiated by the Commission by proposing legislation. The Council of the European Union (which consists of member state government representatives) discusses the proposal and adopts a "negotiating mandate" (or not), which is the allowed negotiation space the Council's presidency has to negotiate with Parliament about the proposal.

If such a mandate is given, a trilogue between Commission, Council and EU Parliament usually starts.