What is referred to as any distinct variety of a language, especially one spoken in a certain region or part of a country?

The term that describes any distinct variety of a language, particularly one that is spoken in a specific region or part of a country, is "dialect." Dialects encompass differences in vocabulary, grammar, and pronunciation among speakers of the same language. They can reflect the cultural, historical, and social influences of the region in which they are used.

For instance, in English, there are numerous dialects like Southern American English, Cockney, or Geordie, each characterized by unique linguistic features. Understanding dialects is essential for appreciating the richness of a language and how it adapts to different communities.

The other options refer to different concepts: "language" is a broad term that refers to a system of communication, "accent" specifically deals with pronunciation variations, and "vernacular" typically indicates the native language or dialect spoken by people in a particular region, often used in contrast to a formal language. While related, these terms do not capture the distinctiveness associated with dialect as effectively as the correct answer does.