Google dance is when your site is very new and google tries to find it's place on the page. This will affect your search engine ranking for the moment, but after google finds your website's place on the page you will came back where you have been in the tfirst place or better.
Google Dance happens when your building backlinks concious or unconcious and google is trying to determine its SERP rank for your site. As previous poster said, nothing to worry about.
After the caffeine update Google has started updating its index on regular basis... which is why dancing does not exist anymore.
just like it sounds dont matter if its an old site or new when you do seo to it such as backlinks its going to cause you to go up and down in the serps till it settles.
sometimes your ranking keyword fluctuate and it goes at down side suddenly that is called google dance.
Simply fluctuation in ranking. When your site rank ups and down in the search engine and can't get in a fixed ranking then it'll be termed as Google Dance. Any site can be affected by it and such situation is not stable so not to worry.
this website has some good advice on what the google dance is- http://www.metamend.com/google-dance.html