A focus edit, sometimes referred to as a crossfade edit, is an improvisational edit employed in longform.
A scene is going on. An offstage improviser walks on and begins their new scene, clearly indicating that they are in a different reality than the previous scene. Just as a sweep edit is not interpreted as another character entering and running through the scene, a focus edit is not interpreted as another entrance. By making use of different tonality, physicality, or content for the scene, an improviser employing a focus edit makes it clear that they have not entered the existing scene but instead begun a new one.
A focus edit seeks to make transitions in improv shows more subtle. They are often employed by ensembles who believe that the sweep edit is confusing to audiences who aren't used to seeing improv.