The article is devoted to the problem of essential ambiguity and fuzziness of the 'loyalty' concept. To solve this problem, the necessity of meaningful differentiation of the concept of 'loyalty' with conjugate and related concepts is emphasized. A comparative analysis of the often confused terms 'loyalty' and 'commitment' is carried out. The possibility of extrapolating the obtained results to the interrelation of the  similar Russian terms 'loyalty' and 'commitment' is analyzed. The following rules for the scientific application of comparable terms are recommended: 1) the term 'loyalty' is relevant to use only in the context of personal-group relations, and the term 'commitment' - also outside it; 2) the term 'loyalty' is applicable only to indicate relations of the 'subject-subject' type, which is possible only in the relations of the individual with his membership groups, characterized by real psycho-behavioral unity, and the term 'commitment' is applicable for indicating relations of the 'subject-object' type as applied to any groups; 3) the term 'loyalty' is applicable when considering the relationship of a person with a group as a system in all of its psycho-behavioral aspects taken together, the term 'commitment', applied in a person-group context, can reflect a person's attitude to single characteristics of the group; 4) psychologically, the term 'loyalty' is more appropriate to use to characterize the person as a whole, and the term 'commitment' - to characterize particular features of the person; 5) specifying displays of total regulation of behavior by norms of group, with which there a person identifies himself and forms actual partnership, it is recommended to use the term 'loyalty', and the term 'commitment' is better suited for describing the actions related to individual choices and decisions of the person not reflecting his orientation and social self-identification. The topicality of the term 'loyalty' is noted for systematic conceptual research, which studies person in a group, and the term 'commitment' is important for applied research on specific forms of social behavior.