Fast change in SERP is called google dance.
The name "Google Dance" is often used to describe the index update of Google search engine. Google index update occurs on average once a month. Can be identified by significant movement in search results and, especially Google's cache of all indexed pages reflecting the status of the last Google crawl. However, the update does not proceed as a switch to another index at a given time. In fact, it takes several days to complete the update of indexes. During this period, the old and the new index alternate on [url]www.google.com[/url]. In a first stage, the results of the new index occur sporadically. But later, appear more frequently.
Google Dance" was in the past used to describe the period that a major index update of the Google search engine are being implemented. These major Google index update occured on average every 36 days or 10 times per year. It was easiest be identified by significant changes in search results, and by an updating of Google's cache of all indexed pages. These changes would be evident from one minute to the next. But the update did not proceed as a switch from one index to another like the flip of a switch. In fact, it took several days to finish the complete update of the index.
At any time during an index update you can check the Google servers, and they will display sometime wildly differing results, thus they are said to be dancing, and hence the name Google Dance. A change in increment and decrement of Google ranking is called as Google dance.
It is the change in ranking in search engines, sometimes frustrating and sometimes overwhelming the mind is a Google dance. While tracking my position, I experienced my own, sometimes I'm on page 3 and day 7 after 4 go to back in one day and so on.