The meaning of “Remastered”

A lot of music I already have is being re-released and “remastered”.  Some of those contain new tunes or printed material and I might buy (again) just to have that.  Otherwise, what’s the value of a new master?  I remember direct to disc vinyl was said to be limited to 10,000 copies because the “master” from which copies were pressed, wore out.  Tape masters would have physically limited lifespans, too.  But in the age of digital music, what is a remaster?  I suppose a new release could have been “re-mixed” or “re-normalized”, so there may be real sonic differences which may or may not be an improvement.  Does the use of the term mean there is some actual audible voodoo by an engineer rather than just procreation of an existing audio file?