In the summer of 2003 Google switched to a “fresh crawl” process to make their results as relevant and as fresh as possible. It runs each day. The purpose of the daily fresh crawl is to update Web pages in the index that change regularly.
This allows Google to provide results that are up-to-date with current events, generating much smaller day-to-day changes that some people called everflux.
We have qualified below various other descriptions of search engine updates. Provided by Matt Cutts, Google:
Algorithm update: Typically yields changes in the search results on the larger end of the spectrum. Algorithms can change at any time, but noticeable changes tend to be less frequent.
Data refresh: When data is refreshed within an existing algorithm. Changes are typically toward the less-impactful end of the spectrum, and are often so small that people don’t even notice. One of the smallest types of data refreshes is an:
Index update: When new indexing data is pushed out to data centers. From the summer of 2000 to the summer of 2003, index updates tended to happen about once a month. The resulting changes were called the Google Dance. The Google Dance occurred over the course of 6-8 days because each data center in turn had to be taken out of rotation and loaded with an entirely new web index, and that took time.
