What is a 12 line poem called?

Understanding 12-Line Poetry

A poem consisting of 12 lines is often termed a dodecasyllabic piece or a dodecasyllable. Moreover, there are distinct poetic structures that encompass 12 lines, each with unique titles, such as the Sonnet (which is typically 14 lines but may also be adapted to a 12-line version) and the Rondeau, which features a different structural approach.