Remaster (also digital remastering and digitally remastered) refers to changing the quality of the sound or of the image, or both, of previously created recordings, either audiophonic, cinematic, or videographic.
Remastering is the process of making a new master for an album, film, or any other creation. It tends to refer to the process of porting a recording from an analogue medium to a digital one, but this is not always the case.
For example, a vinyl LP – originally pressed from a worn-out pressing master many tape generations removed from the "original" master recording – could be remastered and re-pressed from a better-condition tape. All CDs created from analogue sources are technically digitally remastered.
The process of creating a digital transfer of an analogue tape remasters the material in the digital domain, even if no equalization, compression, or other processing is done to the material. Ideally, because of their higher resolution, a CD or DVD (or even higher quality like high-resolution audio or hi-def video) release should come from the best source possible, with the most care taken during its transfer.