A line is a unit of writing into which a poem or play is divided: literally, a single row of text. The use of a line operates on principles which are distinct from and not necessarily coincident with grammatical structures, such as the sentence or single clauses in sentences. Although the word for a single poetic line is verse, that term now tends to be used to signify poetic form more generally.[1] A line break is the termination of the line of a poem and the beginning of a new line.
The process of arranging words using lines and line breaks is known as lineation, and is one of the defining features of poetry.[2] A distinct numbered group of lines in verse is normally called a stanza. A title, in certain poems, is considered a line.
Some critics go so far as to say that lineation is the defining characteristic of poetry, and many would say it's certainly one major difference between most poetry and prose.