What is the term for a group of verses covering one main topic in a work of poetry?

The correct term for a group of verses that covers one main topic in a work of poetry is "stanza." Stanzas function similarly to paragraphs in prose; they organize thoughts and ideas within the poem and help to establish a rhythm and structure. Each stanza can explore different aspects of the main topic or provide a thematic shift, creating a cohesive sense of progression throughout the poem.

The other options do not accurately describe a grouping of verses in poetry. Plot refers to the sequence of events in a narrative and is applicable in prose rather than poetry. Characters are the individuals who are part of a story, typically found in narratives, and not relevant to the structure of poetry itself. A monologue is a speech delivered by one character, which does not pertain to the organization of verses in a poetic context.