Definitions for "Google dance"
The update of the Google index, which takes place every 20-30 days.
During a Google update, the SERPs returned by Googles various datacenters are different, some showing the new SERPS and some showing the old ones. The SERP placement of a site will change from minute to minute and this is referred to as Google "dancing"
When Google updates its nine data centers, the positions of the sites appear to dance as they fluctuate from minute to minute. This fluctuating positions, when Google is performing it index update, are unofficially termed Google Dance. Simply put, when Google updates its index, it is called Google Dance.