Let’s be clear about this, the Google dance is not really a dance or some fun new craze, it’s actually much more serious. The Google dance is what happens during the few days each month when Google updates its PageRank (the website popularity index). It’s by performing the Google dance that Google decides on the order in which links to websites, blogs, forums, etc. will appear in its pages. This Google update process takes several days, as calculating the PageRank (PR) is a complex process. While the updating of the PR is in progress, the position of a particular website on Google may vary from one minute to the next. Depending on the calculations done to arrive at the PR, a website might either go up or down on the pages of Google. Three or four days are needed for its position to stabilise.
The Google dance is very destabilising for website publishers and bloggers, as it can raise false hopes or create disappointments. Since 2002, the frequency of Google dances has been stepped up, and the PR is now updated almost in real time (every15/20 minutes). That said, the term is still sometimes used to mean updates to the algorithm, which the search engine does every 3 or 4 months. So if your website has gained a point in terms of PR, you can say, "After the last Google dance, my website went up one point, now it’s at 5".