deiyezooger:
There is something called a mitzva tantz. I have never seen one. It is a chassidish minhag, and is considered very holy. One YWN poster even said it is more important than the whole wedding.
Whatever distinguishes it from the rest of the wedding and from regular normal custom, is the topic of this thread. That certainly includes holding the gartel, and also includes the patterns traced by the dancers, which I am told spell Hashem’s name.
It was suggested that that stemmed from the machzor vitri, but that was clearly erroneous.