A rainbow kiss is a sexual act involving two partners simultaneously engaging in oral sex when the female partner is menstruating. After the act, the partners kiss, mixing menstrual blood and semen in their mouths, which creates the visual metaphor of a "rainbow." This act is sometimes discussed in the context of taboo or niche sexual practices and has gained attention in recent years through social media platforms like TikTok. It emphasizes a form of intimate exchange that combines physical pleasure with a display of trust and acceptance between the partners.