The definition of 'digital' music is music which is either created, or recorded and stored electronically.
The standard use of the term 'digital' is to distinguish it from 'analogue', and the fundamental differences betwen those two is that analogue is usually recorded on a reel-to-reel tape machine, and digital is recorded directly onto a computer drive.
A more encompassing adjective 'digital music' is used to describe music which is created entirely electronically such as Kraftwerk, Jean Michel Jarre, Tangerine Dream and so on, and could be extended to Westlife, because they are robots.