What does "fade in" mean?

What does fade in mean? Fade in means to gradually appear, increase in intensity, or become visible or audible from nothing. In film and video, fade in is transition where image gradually emerges from black, beginning of scene, opposite of fade out. In audio, fade in means sound or music starts at silence and gradually increases to normal volume, often at beginning of track. As verb phrase, to fade in means to cause to appear gradually. In lighting, lights fade in means brighten slowly. Figuratively, memory fading in means returning gradually. Synonyms include emerge, appear, brighten, and swell. Opposite is fade out, where something disappears gradually. In everyday use, hope fades in means returns gradually. In haircut, fade in is not standard, but blending can be described. In presentation, slide fades in means transition effect. So fade in conveys gradual, not sudden, appearance or increase, whether visual image brightening from black, sound increasing from silence, or presence becoming more noticeable, used intentionally in media editing to create smooth start rather than abrupt cut, providing gentle introduction to scene or sound.