Duet

A Duet puts two videos in one frame, the original on one side and your camera on the other, both playing at once. Creators use it to react, answer, harmonise, argue or land a punchline, and the format is a large part of how an idea travels across TikTok instead of staying on one account. Duets can be turned off per video or account-wide in the privacy settings.

The word has escaped the app, so people say duet for the same thing anywhere. On YouTube Shorts that feature is Collab and on Instagram the closest equivalent is a Remix, both of which behave slightly differently.