From an Esquire Magazine essay in the 1930s entitled "Essay on Jiggling," I give you the wisdom of George A. McNamara:
Although the meaning of the word is clear and definite, it is difficult to describe the jiggle because it is an integral part of the intricate succession of exercises by which women propel themselves from one spot to another. ... A jiggle occurs when some portion of the body, having been left behind when a major portion was in motion and wishing to catch up, gives a sprightly bounce. In its anxiety not to be left alone, it overleaps its proper position and finding itself without support from the main body, it quickly retires too far, whereupon a secondary jiggle ensues. It is all liveliness and eagerness and gaiety. And as some parts are sliding back while others are catching up, each in its own tempo and arc, yet all somehow holding to the central movement, the effect is indescribably spirited and jolly.
To illustrate, I offer the efforts of Suzanne Pritchard:
Sadly, these efforts were not (to the best of my knowledge) ever captured properly in motion.