crossfade

Short definition from Wiktionary

Noun

1. 1
   A fade in which the volume of one audio track is lowered as that of another is raised.
2. 2
   A fade in which the picture of one video track is diminished as that of another is brightened.

Verb

1. 1
   To lower the volume of one audio track while raising that of another, so that they blend together.
2. 2
   To diminish the picture of one video track while raising that of another, so that they blend together.
3. 3
   To be under the influence of multiple psychoactive substances at the same time; most typically marijuana and alcohol.