Digital remastering is a marketing buzzword for a transfer
of video and/or audio from an analog source to a digital target
using filters. The expression is likely to be used when a movie or
recording was released before for home use in a crappy version and a
new version tries to come closer to the original experience.
One reason to remaster is the availability of a better transfer
technique as used before. Another is the appearance of a source that
is closer to the master recording as the one used previously. (And
where, one is tempted to ask, did they find that and why didn't they
use it in the first place? Well, don't let me start ranting about DVD
Special Editions (with lots of bonus material) of movies that I
already own in not-so-special editions.)
Another reason is the use of digital filters to fix a deficiency
of the original material, e.g. video or audio noise, by removing it
(at least to a degree) or converting it into something less noticeable
or annoying. In case of film, the differing frame rates of film (24
fps) and video (30/60 fps for NTSC, 25/50 fps for PAL)
contribute, among other factors, to a change in color intensity, that
has to be cunningly (color) corrected.
The result is a digital copy that is hopefully as good as the
analog original, and won't degrade any further. It doesn't matter if
the copy is then transferred to analog tape again, the result will
still be called digitally remastered.