Classification of pores is one of the basic requisites of comprehensive characterization of porous solids. There are various categorizations of pores described in the literature, but it is difficult to give a consistent global classification of porous substances including catalysts, adsorbents, oxides, carbons, zeolites, organic polymers, soils etc. The purpose of each of these classifications is to organize pores in classes by grouping them on the basis of their common characteristics like structure, size, accessibility, shape etc. In this study, a summary of the most used classifications of porous materials is done. Some common properties or behavior for individual classifications could be found, but many differences mainly in pore size are still subject of intensive discussions. Therefore, it is the purpose of this review to provide a general description of the concept and classification of pores in porous solids, to deal with complexity of the matter and to organise our knowledge in decision-making proccesses of pore characteristics determination.