A stanza is a group of lines within a poem, usually set off from others by a blank line or indentation. It is a unit of poetry composed of lines that relate to a similar thought or topic, like a paragraph in prose or a verse in a song. Stanzas can have regular rhyme and metrical schemes, but they are not required to have either. There are many different forms of stanzas, ranging from simple four-line quatrains to more complex forms like the Spenserian stanza. Fixed verse poems, such as sestinas, can be defined by the number and form of their stanzas. In music, groups of lines are typically referred to as verses, while the stanza in poetry is analogous with the paragraph in prose.