Good Soldier Schweik, to be precise when discussing non-standard (non-classical) guitar tunings, we would need to differentiate between open tunings - open C, open D minor, etc. - that are tuned to a chord, and alternative tunings - CGCDAB, Orkney tuning, etc. - that are not tuned to an open chord. DADGAD is an interesting one, as it's neither an open major nor minor chord (since the third is missing), but it is open Dsus, if we wish to call it that, so that could argueably qualify as an open tuning or an alternative tuning.