So what is an 18th century polonaise?

For a long time I've thought that the term 'polonaise' referred to the way the gown's skirts were tied up. My research now indicates that it is actually how the back is created - as well as the skirts being tied up, the back is made with a centre back seam and two side seams like a man's coat. There is a fitted bodice underneath an overbodice that flows into the skirt.

Norah Waugh states in Cut of Women's Clothes on pg 73 that the robe à l'anglaise was often equipped with tapes to draw up the skirt, and on the topic of the polonaise says:

Though this term is often applied to any eighteenth-century dress with back drapery, it belongs, strictly speaking, to an over dress that appeared c. 1775. This was cut like the man's coat of the same period, with centre back and two far-back side seams all terminating in inverted pleats, the front being in one piece with an underarm dart. It was caught to the top of the bodice centre front ...