A rather obscure reference to a guitar technique
, or just about any instrument. To be honest, I read it once in a Guitar World
magazine, and only saw it twice after that, in some notes given to me when I learned how to play Moonlight Sonata
A chordal turn refers to a change in the chord structure of a song, taking the song to a new place, an unexpected change. As a for-instance, I'll use the example of Selling The Drama, by Live.
The chords are quite simple, being in D. That is to say, all the chords in the verse - as opposed to chorus - all accompany the D major chord well. It goes G, D, G, D, Em, Bm.
But then, after the B minor chord, a C, or a Csus9, depending on how you play it, is used. This is called a chordal turn, when that unexpected chord is played, taking the flow of the song in a different direction. The use of the D#maj7 barre chord (Or the E flat maj 7. I'm afraid I don't know how to type the little 'b' shape) in Plush, by STP, is also an excellent example of a chordal turn.