this can more commonly be referred to as the "Tuck and Push" - a tip I gleaned from Jeela (aka Annette Mason), a lovely dancer from Arizona.
Just like a tennis player has a "ready" stance, so they can easily reach the ball in any position, also a bellydancer has a neutral ready position to easily enable their body to get back to a stance for the next move.
Here's how to do get the tuck and push working for you (from Jeela's website):
What is this Tuck & Push??
It is the balancing of the front and back of the torso creating a foundation for good posture and power in your dance. It also makes you look great in pictures!
1. Stand with feet hip distance apart, knees soft, weight centered over the arches of your feet.
2. Roll shoulders up, back and down.
3. Use your lower abdominal muscles to pull your belly button in towards your spine: this is your Tuck
4. Use your upper back muscles to draw shoulder blades together and Push rib cage straight forward out over your hips.
5. Hold. Feel your torso lengthen and your chest open.