drop D tuning
A guitar tuning where the lowest string is tuned down one whole step from E to D.
In Depth
Drop D is the most popular alternate tuning in rock and metal. Lowering the sixth string to D enables power chords to be played with a single finger across the bottom three strings, making fast chord changes effortless. It also extends the guitar's low range and creates a heavier, darker sound. Grunge, nu-metal, and modern rock rely heavily on drop D.
Dear Prudence by the Beatles (1968) is one of the earliest famous uses of drop D tuning in popular music, though it was common in classical guitar centuries earlier.