When you flip over the pillow because it's too hot and you want to lay your face on the cool side.
Teddy flipped his pillow over because he had a bad case of hot pillow.
The pillow that's been pulled out from under a woman's buttocks, used during sex to lift her hips and bum up slightly for better penetration and stimulation. It can then be used to lie one's head on, giving immediate warmth for the face and as an added bonus, additional scent.
After a great session, Milo was exhausted, so he pulled out the hot pillow from under Sharon's ass and lay his tired head down to rest. He was asleep in seconds, having been totally overcome by her transferred warmth and overpowering scent.