Which term refers to a regional variety of a language distinguished by vocabulary, spelling, and pronunciation?

The term that refers to a regional variety of a language distinguished by vocabulary, spelling, and pronunciation is dialect. Dialects encompass the unique features of a language that can vary not just geographically, but also socially within certain communities. This includes distinct words and phrases that may not be used or recognized in other regions, as well as variations in spelling that reflect local usage. Additionally, pronunciation differences—such as vowel shifts or consonant articulation—are characteristic of dialects, further enhancing their uniqueness.

In contrast, accent refers specifically to the way words are pronounced and does not necessarily include variations in vocabulary or grammar. Slang consists of informal, often specialized language that can change rapidly within groups and does not represent a broader regional variety. An idiom is a phrase whose meaning is not directly related to the literal meanings of its components, and it is not defined by regional characteristics in the same way a dialect is. Therefore, the correct answer is rooted in the comprehensive understanding of what a dialect encompasses.