What is a common structure of poetry that consists of grouped lines?

The structure referred to in the question is typically defined as stanzas. Stanzas are essentially units of lines within a poem that are grouped together, often separated by spaces. This organization helps to create rhythm, flow, and thematic breaks within the poem, making it easier for readers to follow and understand the ideas being presented.

While free verse refers to poetry that does not adhere to a specific rhyme scheme or meter, it can still have stanzas; thus, it doesn’t specifically define the structure being asked about. A ballad represents a specific form of narrative poetry often with a musical quality and usually follows a particular rhyme scheme and meter, making it more restrictive than simply describing a grouped line format. A sonnet is a specific 14-line poem with a strict rhyme scheme and syllabic structure, which focuses on content and form rather than simply being a collection of lines. Therefore, when defining a common structure of grouped lines in poetry, stanzas are the accurate term.