An organizational pattern in poetry where elements follow an ABBA arrangement, most commonly referring to rhyme scheme but also applicable to thematic or syntactic patterns. In rhyme, the first and fourth elements match while the second and third match, creating a chiastic or mirrored structure. This enclosed pattern creates unity and balance, giving a sense of completion and symmetry. The structure can also refer to thematic development where ideas introduced in the beginning are revisited in reverse order at the end.

ABBA structure is synonymous with enclosed rhyme, commonly found in Petrarchan sonnets and certain hymns; it provides a sense of containment and symmetry, useful for expressing complex or contrasting ideas within a tight frame.