A video transition is a technique used during the post-production process of film or video wherein separate shots or scenes are combined in order to present a cohesive whole. Commonly, especially with film, this is usually just in the form of a "cut," which leads directly to the next scene without any particular visual cue except that the scene has changed. For digital video, the transition can be more visual and obvious such as fade-outs, wipes, dissolves and fades or other visual effects.
Techopedia explains Video Transition
A video transition is used to convey to the viewer that the scene has changed and that another point of view in the narrative is being told or that simply the angle from which the scene is being viewed has changed in order to convey scale or atmosphere. But at the simplest core, a video transition is simply a join in two separate shots.
The goal of a video transition is to seamlessly integrate different shots so that the core narrative moves forward believably and that it does not distract the viewer. This is especially true for movies and cinema, but for amateur videos that tend to be more lighthearted, video editing software provides different kinds of video transitions, which are usually very animated and colorful, complete with sound. Transitions such as fly-ins and spiral-ins can be fun to watch at times, but can become distracting and obstructive if used incorrectly.