The paper presents a review of and a comparison between some selected definitions concerning the issue of food  loss and food waste as formulated by representative institutions and organizations at the global and European level. The regulative principle of sustainable and sustainable development enjoins to counteract food losses and  food waste and its target numbered as 12.3 is to reduce them by half by 2030. In the paper, the focus is on the definitions of terms such as food, food losses and food waste including also: natural decrease in food, by-products, and food waste, i.e. on the definitions developed under the FLW Standard and FUSIONS projects. Based on the analysed and cited approaches, it can be concluded that those terms may be differently understood and defined depending on the needs, objectives and area of the planned applicability of a given definition. There are noticeable discrepancies in determining the starting point for measuring losses and wastage. On a global basis, they also should be taken into account at the pre-harvest stage while, on the European basis, they can only be counted at the post-harvest stage, when the agri-food chain starts. Additionally, a different approach applies to by-products – according to FAO, they should be treated as food loss and food waste and according to the definition as adopted in the EU directive, they are neither a food loss nor a food waste. So the subject and extent of their measurement depend on the definition of key terms and categories related to the problem of food losses and food  waste. Those issues should be taken into account in research methodologies for measuring and monitoring  losses and wastage including food waste. In May 2019, at the EU level, respective guidelines were adopted in  the delegated decision of the European Commission; those guidelines referred to a common methodology of and  minimum quality  requirements for the uniform measurement of food waste levels.