When a character lies flat on their stomach with their feet up in the air.
This is usually done to show off a character's breasts, ass, and feet all at the same time. The subject can be wearing legwear or barefoot, but their feet must be visible as this is a term coined by foot fetish enthusiasts to describe a particular pose that shows off the feet.
The Pose is one of the most requested positions in foot fetish history, and can be found in droves on such fora as Yuku's TheMousepad, Wu's Feetlinks, and others.
This tag implicates on_stomach (learn more).