Fade
A common type of transition in both video and audio.
In a video fade-out, a clip begins at full image intensity and then diminishes in intensity until it disappears. In a video fade-in, a clip ramps up from zero intensity to full visibility. These are the common “fade to black” and “fade up from black” transitions.
Audio fade-ins begin with silence and increase to full volume, and fade-outs begin at full volume and decrease to silence.