The dash (-) vs. plus (+) difference is about competing standards developed by different industry groups in the late 1990s/early 2000s. DVD- (minus) was backed by the DVD Forum, while DVD+ (plus) was backed by a separate alliance including Sony and Philips. Kind of like what happened earlier with Betamax and VHS.  In practice, most modern DVD players and drives handle both just fine, but some older or specialized equipment require certain discs.

The R vs. RW difference:

  • DVD-R and DVD+R — “R” stands for recordable. You can write to these once, and once only. After that, the data is permanent. Think of it like a piece of paper you write on with permanent marker — great for archiving movies, backups, or anything you won’t need to change.
  • DVD-RW and DVD+RW — “RW” stands for rewritable. These can be erased and re-recorded hundreds of times. More like a whiteboard. Useful if you want to reuse the disc, though they tend to be a bit more expensive than their write-once counterparts.

Caviat:  Some medical imaging equipment specifies the disc to use.  Some equipment that specifies DVD+RW can be used with DVD+R discs.  Testing is required to confirm.