TikTok's feature for combining videos side-by-side is called Duet. It creates a split-screen layout in which a new video appears alongside an existing TikTok, often using the original video's audio.
Duet became one of TikTok's signature forms of participation because it lets users respond to, perform with, or react to another creator without making a conventional reply. Musicians can sing harmonies, comedians can add punchlines, and educators can respond to demonstrations or explanations. The original creator's video remains visible as part of the paired composition.
Duet is not the same as Stitch. Stitch incorporates a selected segment of another video into the beginning of a new one, whereas Duet presents the two videos simultaneously in a split-screen arrangement. “Remix” and “Collab” may describe similar ideas on other platforms, but Duet is TikTok's canonical feature name.
Creators control whether their posts can be used in Duets. Availability also depends on account age, privacy settings, regional rules, and whether the original poster has enabled the option. Those controls do not change the feature's standard name.