Mixolydian

Mixolydian is the 5th mode of the major scale (step pattern W – W – H – W – W – H – W; from G: G – A – B – C – D – E – F). Major with a flatted 7th (b7) — bright and bluesy. The dominant chord turned into a tonal center with a rock/folk edge.

Like major (Ionian) with one alteration: b7. The lowered seventh turns the VII chord into a major triad (bVII), creating the back-and-forth motion that defines rock and blues harmony.

Where you hear it: "Sweet Home Chicago", "Norwegian Wood" (Beatles), Celtic and folk music — anywhere a major sound needs a darker, looser edge.