In  poetry, metre (meter in US spelling) is the basic rhythmic structure of a verse or lines in verse. Many traditional verse forms prescribe a specific verse metre, or a certain set of metres alternating in a particular order. The study and the actual use of metres and forms of versification are both known as prosody. (Within linguistics, "prosody" is used in a more general sense that includes not only poetic metre but also the rhythmic aspects of prose, whether formal or informal, that vary from language to language, and sometimes between poetic traditions.)