What does bridge to D mean in guitar music?
I’m not sure, but it possibly means pulling an accessory known as a “D-Tuna” on the bridge which immediately drops your low E to a D. And if its popped back in, it brings you back up to an E. The only reason drop D is popular is because it makes power chords (the 1st and 5th) easier, only using one finger to bar instead of using two in standard tuning.