What is defined as a group of lines forming the basic recurring metrical unit in a poem?

A group of lines that forms the basic recurring metrical unit in a poem is referred to as a stanza. Stanzas serve as the building blocks of poetry, much like paragraphs in prose, and they can vary in length and structure. Each stanza often encompasses a specific idea or theme, contributing to the overall movement and message of the poem. The repetition of stanzas can create rhythm and enhance the auditory quality of the work, making it more engaging for the reader.

In contrast, vocabulary pertains to the words used in a language or text and does not specifically relate to the structure of a poem. Rising action is a term from narrative structure that describes the events leading up to the climax of a story, not applicable to the unit of a poem. The topic is the main subject or theme of a piece of writing, which, while relevant to understanding the poem's content, does not define the structural aspect represented by a stanza.