Heartfelt phrase

…5･7･5･7･7 is divided into the top three lines (5･7･5) and the bottom two lines (7･7), the former are called the upper line (kami-no-ku) and the latter the lower line (shi-no-ku). The first line (5) is called the first line, head line, or opening line, the second line (7) the chest line, the third line (5) the lower line, and the fifth line the conclusion line, tail line, or closing line. A composition that does not fit the 5 lines and 31 beats is called "out of rhythm," one that is too long is called "too many characters," and one that is too short is called "not enough characters." …

*Some of the terminology explanations that mention "muneku" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…5･7･5･7･7を上3句(5･7･5)と下2句(7･7)とに分け，前者を〈上句（かみのく）〉，後者を〈下句（しものく）〉と呼ぶ。第1句(5)を初句，頭句，起句，第2句(7)を胸句，第3句(5)を腰句，第5句を結句，尾句，落句などと呼んでいる。5句31拍に合わない作を〈破調〉といい，長すぎるものを〈字あまり〉，短いものを〈字足らず〉と呼ぶ。…

※「胸句」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報