the pose
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.
See also
This tag implicates on_stomach (learn more).