"Red thoughts" is a term used on TikTok to describe a romantic or sexual scenario that someone wants to experience with someone else. The term is often associated with TikTok slideshows and is characterized as lustful and sexual thoughts that go through ones mind while thinking about someone. It is a trend on TikTok where users create videos with captions that describe their "red thoughts" and set them to music. The trend has gained popularity on the platform, with many users participating and sharing their own "red thoughts" videos.