fade in

Short definition from Wiktionary

Noun

1. 1
   A type of transition used in visual media, in which the transition is at first black, fading to a visual image.
2. 2
   Alternative form of fade in.

Verb

1. 1
   To fade from black to a visual image in a film or other visual media.
2. 2
   To commence with silence in a song and then slowly increase the volume of the music until the intro of the song is over.