What is a fixed number of lines of verse forming a unit of a poem called?

A fixed number of lines of verse that forms a unit of a poem is known as a stanza. Stanzas serve as the equivalent of paragraphs in prose; they allow poets to organize their ideas and create a structure within their work. Each stanza can vary in length and rhyme scheme, helping to convey different themes or emotions throughout the poem. The term "stanza" comes from the Italian word for "room," which interestingly suggests different sections within a larger structure.

The other terms listed do not relate to this concept. A soliloquy refers to a device often used in drama, where a character speaks their thoughts aloud, usually when alone, which doesn't pertain to poetry structure. A parody is a humorous or satirical imitation of a particular genre or work, rather than a structural element of poetry. Sanction typically refers to official approval or a penalty for disobeying a law, making it unrelated to poetic terminology. Thus, "stanza" is the most appropriate term for a unit of verse in a poem.