Cross-fade (Wikipedia) in audio engineering is a transition between two tracks playing at the same time by fading one out and another one in.
- A particularly interesting use case for it is for tracks that have the exact same structure but different variations, e. g. instruments, in this case cross-fade preserves the motif but significantly changes the character of the track at will of the performer, sometimes almost imperceivably. This effect is sometimes used in video games to make the music more interactive.
- It can also be used for “gapless playback”, where the end of one track is cross-faded with the start of the other.
While these two scenarios are common uses of this technique, neither of them define it.