The author analyses the problem of ambiguity contained in the definition of intra-industry trade i.e. the simultaneous import and export of goods from the same industry and shows that the definition of intra-industry exchange of goods is applied to different trade streams. In such context, definitions applied to branches of industry also tend to vary. Such an approach results in difficulties with respect to the definition of the factors that affect the intensity of the intra-industry exchange and measuring the size of trade operations. Since the problem described in the article arises at the point of junction between the theory of economics and empirical research, the considerations are preceded by a short analysis of selected aspects of an argument between theoreticians and empiricists and the presentation of theoretical explanations regarding the genesis of international trade.