Phrygian
Definition
The third mode of the major scale; equivalently natural minor with a flattened second (1 b2 b3 4 5 b6 b7).
Why it matters
That b2 against a root power chord is one of the fastest ways to change a riff’s color.
Examples
Riffs that neighbor the root from a half-step above; phrygian dominant when the 3rd is major instead of minor.