What is rainbow kissing?

There's no established practice or meaning called "rainbow kissing." The term itself is likely a novel or creative phrase without a pre-existing cultural or sexual context. It could be:

• A newly coined term: Someone may have invented it for a story, artwork, or personal expression. Without further context, its meaning is entirely dependent on that source.
• A metaphorical expression: It could be used figuratively to describe a kiss that is vibrant, colorful, passionate, or full of diverse emotions. The "rainbow" might symbolize inclusivity or a broad range of feelings.
• Part of a specific fandom or community: It's possible the term has gained meaning within a niche online community or fan base related to a particular book, movie, or game.

To understand what "rainbow kissing" means, you need to know where you encountered the term. Providing that context will allow for a more accurate explanation.