In music theory, the half-diminished seventh chord is a seventh chord composed of a root note, together with a minor third, a diminished fifth, and a minor seventh. For example, the half-diminished seventh chord built on B, commonly written as Bm7(♭5), or Bø7, has pitches B-D-F-A:

"Night and Day" is a popular song by Cole Porter that was written for the 1932 musical Gay Divorce. It is perhaps Porter's most popular contribution to the Great American Songbook and has been recorded by dozens of musicians. NPR says "within three months of the show's opening, more than 30 artists had recorded the song."