Open D is a guitar tuning where the strings are adjusted to create a D major chord when played open, without pressing any frets. In this tuning, the strings are typically tuned to D-A-D-F#-A-D from the lowest to the highest string. This allows for rich, resonant sounds and is often used in folk, blues, and rock music. Musicians appreciate Open D for its ease of playing and the unique harmonic possibilities it offers. It enables players to create beautiful slide guitar melodies and open chords, making it a popular choice among artists like Robert Johnson and Derek Trucks.