chōonpu

thumb|190px|The word (, ) written vertically with vertical chōonpu The , also known as , , , or Katakana-Hiragana Prolonged Sound Mark by the Unicode Consortium, is a Japanese symbol that indicates a , or a long vowel of two morae in length. Its form is a horizontal or vertical line in the center of the text with the width of one kanji or kana character. It is written horizontally in horizontal text and vertically in vertical text (ー). The is usually used to indicate a long vowel sound in katakana writing, rarely in hiragana writing, and never in romanized Japanese. The is a distinct mark from the dash, and in most Japanese typefaces it can easily be distinguished. In horizontal writing it is similar in appearance to, but should not be confused with, the kanji character ("one").

The symbol is sometimes used with hiragana, for example in the signs of ramen restaurants, which are often written in hiragana, while the most standard orthography would be in katakana: . Canonically, however, hiragana never uses the ; instead, another vowel kana is used to express the long vowel. This applies in theory to onomatopoeia written in hiragana as well, but the use of the is generally tolerated and common: for .