The term Belly Dance is actually a misnomer. It is a dance style that uses the torso and hips but rarely the 'belly'. The term came about from the Chicago World Fair in 1893 when it was thought it would pull the punters more than a more neutral label. (We are talking Victoria era when even legs were considered risque).
In Arabic it is called raqs sharqi - dance of the east; in French danse orientale. This dance has the potential to become the visual dimension of the music and as such is often best expressed as an improvised solo.
It is a dance form with a rich history; blending influences from the folk dances of the Middle East and North Africa with Russian ballet and the fantasies of Hollywood. Its earlier origins are hard to untangle. There are those who say it was linked with the worship of the Goddess or it was an aid to fertility and birth; those who believe it existed only to titillate men; and those who say it was only ever performed by women for women. Each may contain grains of truth but such beliefs function more as mythology than historical fact. What is fact, is that this art form is currently flourishing in the West. In addition to dancers studying the form as it is now and has been presented in the Middle East, there have been a number of innovations including veil work, Tribal, and a more westernized use of space.
So if it can change, what distinguishes raqs sharqi? Many people expect to see a bare belly and lots of sequins - and although bedlah is often worn, the dancer could quite validly be in an evening dress, a tunic, pantaloons, or non-traditional costume. It is not the costume that defines the dance but the style of movement. What the audience sees tends have more emphasis on the torso (especially the hips) rather than travelling steps; the underlying form is built on isolation of muscles groups - often very subtle. The subtlety, control, and posture is what distinguishes Oriental dance from the more folkloric styles and takes many years of study to achieve.
But Middle Eastern Dance is more than raqs sharqi. It is the hip shimmying, foot stomping Ghawazee style or the horse prancing, cane cracking Saidii style - both from Egypt. It is the twisting Tunisian style with water pots balanced on the head. It is the precision of the debke from Lebanon. It is the sultry sway of the beledi bint. Many dancers also study these, and the dozens of other regional variations, which have influenced the form. Some dancers specialize in a region. There is more to learn here than can be achieved in one life time!