On guitar, a form of alternative tuning
where the guitar is tuned lower than the standard EADGBE. Although alternate and open tunings
have been used for many years down tuning has become recently asscociated with heavy metal
bands, who do it to get a weightier sound or compensate for the vocal range
of their singer. Often they will combine this with drop d
Down tuning is not exclusively for metal bands, Hendrix and Stevie Ray Vaughan were known to play at Eb.
A quick list off the top of my head of bands where much of their material is downtuned, I'm using the lowest note as a guideline as it can be hard to tell if an artist has downtuned all the strings or just the first (Please msg me or softlink to more):
Eb: Hendrix, Weezer
D: Tool, Helmet
C#: A Perfect Circle, Nivana(In utero), Limp Bizkit
C: Queens of the Stone Age, System of a Down, Black Label Society
B: Slipknot, Soundgarden, At this point you may as well give up and go buy a seven string guitar, but no one's saying you cant downtune that...
G#: Deftones (The Deftones have a running joke where each of their albums is tuned lower than the last, this was their latest)
The only band I have heard of going lower than this is Meshuggah, who are apparantly using 8 string guitars.