I like to talk about "energy" and originating the energy from your "centre" (a point in the middle of your pelvis, at a height half-way between your pubic bone and your navel) moving that energy up the spine, through the back muscles, and out through the fingertips.
It's all a bit airy fairy and artsy. That's OK, I'm an artist, I get to be artsy.
Sometimes I call the "energy" "intention". It's not the literal tensing of muscles, it is a confident relaxed feeling that the muscle is there, ready to do your bidding.
I have a little secret to share though, it's not really all artsy at all. We are going to have a bit of a delve into the anatomy that I don't really cover in lessons, as frankly, my dance students aren't there to learn anatomy (if you would like to learn anatomy though, I do tutor, contact me for my rates...)
Take a look at these lovely anatomical images.
See in the top one. Can you see how the bones of your arm and shoulder attack to the bones of your "body"? They barely do. The only bone that joins your arm to your torso is that skinny little clavicle, lightly kissing the sternum. It might as well not bother. The clavicle doesn't carry weight, or move the arm, it's just there for stability. Four-legged running types don't even have a clavicle.
So take a look at the bottom one. Meaty huh? All that muscle on your back? That's what keeps your arms on. That's what bears the load, and that is what makes the movement.
OK, so I expect that those of you who don't enjoy looking a drawings of dead people as much as I do probably would like a point. So here it is:
When you hold your arms in basic dance positions, they are supported by the large muscles in your back. Mostly the trapezius (the bright red one). That is where the strain is. If you are trying to use your arm muscles to hold your posture, it will ache, your muscles will tense, you will end up looking like a chicken. Chickens don't bellydance. It's sad, I know, but we can get past that, you are not a chicken, so you can. Consciously bear the weight of your arms with your upper back. Instant improvement.
When you move your arms, again it is those muscles on your back making it happen (they have some friends in other places, but they do plenty of the work). Much like when you move your fingers it is the muscles in your lower arm working. If you envisage the movement starting at the shoulder, you create an artificial disconnect. Reach from your spine, let the movement flow out and down through to your fingertips. Isolate when you need to, but sweeping, fluid arm movements, involve the torso too.
So that's the science bit.