The name "Google Dance" is often used to describe the index update of the Google search engine. Google's index update occurs on average once per month. It can be identified by significant movement in search results and especially by Google's cache of all indexed pages reflecting the status of Google's last spidering. But the update does not proceed as a switch from one index to another at one point in time. In fact, it takes several days to complete the index update. During this period, the old and the new index alternate on www.google.com. At an early stage, the results from the new index occur sporadically. But later on, they appear more frequently. Google dances.
Occasionally I will see search results change around just by hitting refresh. My page will 'bounce' from say 10 to 15 back to 10 and 15.
It's not that only. When Google dance happens, sites get ranked lower. It happnes on a daily basis. Please read this post: Insane traffic building tips It has a small section describing google dance. another post also describes it. please use the search feature to get to that post. Google dance is essentially a google game by which, google merely ranks you lower when your daily search traffic limit is reached. Usually don't you notice that you are actually ranking for a search term which gets 100 searches daily but still you are stuck at 80 daily visits? Even with so many other minor search terms which together can give almost another hundred search visits? It's due to google dance. google controls your visits by ranking your pages lower once your daily stats is achieved. To overcome this issue, only way is posting regularly and getting backlinks and continued seo. I have experienced this effect myself. For instance, I am ranking high for "good writing" which is a search term which gets hundreds of searches, still I don't get more than ten visits daily from that search term from google.