In Italy this liquid is called Colatura, in Spain it is SalMŭria, but by any name it is the liquid which results from the process of salt-curing anchovies over their months long journey from fresh fish to semi-preserved fillets - Anchovy extract Spray.
A little goes a long away,  and this chef’s secret ingredient can be used in myriad ways to add umami and complexity to hundreds of dishes. The spray bottle makes it simpler to get a misting on as a finish flavor.