fade-in

[ feyd-in ]
/ ˈfeɪdˌɪn /

noun

Movies, Television. a gradual increase in the visibility of a scene.
Broadcasting, Recording. a gradual increase in the volume of sound, especially of recorded or broadcast music, dialogue, or the like, usually starting from complete inaudibility.

Origin of fade-in

First recorded in 1915–20; noun use of verb phrase fade in
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

British Dictionary definitions for fade-in

fade-in

noun

films an optical effect in which a shot appears gradually out of darkness
a gradual increase in the volume in a radio or television broadcast

verb fade in (adverb)

Also: fade up to increase or cause to increase gradually, as vision or sound in a film or broadcast
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012