The study of linguistic units operating as part of the national language within the framework of the regional usage is determined by the need to identify the features of heterogeneous variants and their place in the system of the national language, their relationship and interaction with the literary norm. The purpose of this article is to investigate the content of the linguistic term “localism” and distinguish it from other concepts used to denote territorially marked vocabulary. The article attempts to clarify the content of the linguistic term “localism” using examples from the Russian and Spanish languages, which occupies a central place in foreign linguistic regionalism. The theoretical basis of the study relies on the ideas of linguistic relativism and sociolinguistic determinism, according to which linguistic phenomena are studied taking into account variability as a fundamental property of language and in close relationship between language and social context. The methodological base is formed by general scientific methods, includingThe study of linguistic units operating as part of the national language within the framework of the regional usage is determined by the need to identify the features of heterogeneous variants and their place in the system of the national language, their relationship and interaction with the literary norm. The purpose of this article is to investigate the content of the linguistic term “localism” and distinguish it from other concepts used to denote territorially marked vocabulary. The article attempts to clarify the content of the linguistic term “localism” using examples from the Russian and Spanish languages, which occupies a central place in foreign linguistic regionalism. The theoretical basis of the study relies on the ideas of linguistic relativism and sociolinguistic determinism, according to which linguistic phenomena are studied taking into account variability as a fundamental property of language and in close relationship between language and social context. The methodological base is formed by general scientific methods, includingtheoretical analysis and synthesis of linguistic literature on the problem of regional vocabulary, as well as comparative analysis of terms denoting territorially marked language units. In the practical part of the study, the sociolinguistic interview method was used. General characteristics of localisms in Russian and Spanish are revealed. The conclusion about a stricter regulation of the use of localisms in the Spanish language is substantiated.