Final answer:
The described transition is a Fade In, a film technique where a scene transitions from blackness to the next shot, used to convey a change in time or emotion.
Step-by-step explanation:
The transition described in the question is known as a Fade In. This term refers to a film editing technique where the previous shot darkens to blackness, which is the Fade Out part, and then the image gradually lightens to reveal the next shot, which is the Fade In.
This cinematic technique is often used to indicate the beginning of a scene or to signify a transition in time and emotion in the storyline.