Google Dance Tool
During the month, Google sends out robots (spiders) to crawl the web and archive every website it finds. These archived websites will be presented in the next update of the Google index (database). The update process is initiated every 30 days or so, although on some occasions there have been more than 30 days between updates.The Google Dance Tool is provided as a tool to help you, the webmaster, determine when the Google search engine is spidering the internet. This is extremely useful if you want to know when your site(s) will rank in Google.
Google have 3 main www servers online, which are as follows:
www.google.com - The main address, the true homepage of google.
www2.google.com - Thought to be a test server.
www3.google.com - Thought to be a test server.
While nobody outside of "Google" truly seems to know the purpose of the www2 & www3 servers, many people have come to the assumption that they are test servers. During the update, which takes several days, the 3 Google servers display different results. While the results vary from server to server, they are said to be "dancing", hence the name "Google Dance".