"Drop D" is a guitar tuning where the lowest string, the sixth string, is tuned down one whole step from E to D. This creates a deeper, heavier sound that is popular in various music genres, especially in rock and metal. It allows for easier power chords and a more resonant tone, making it a favorite among guitarists. In Drop D tuning, the other strings remain in standard tuning, which means the fifth string is still A, the fourth is D, the third is G, the second is B, and the first is E. This tuning is often used in songs by artists like Nirvana and Tool, providing a unique sound that enhances their music.