Leading up to Webmaster World in Vegas, I geared up the members of SEO Revolution to prepare for the annual algorithm (or filter) update from Google. I was seeing the same type of movements in the datacenters that showed an update was coming … however, an update never came.

I have been wrong before …

Here is a summary of what Matt said:

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. In the summer of 2003 (the Google Dance called “Update Fritz”), Google switched to an index that was incrementally updated every day (or faster). Instead of a monolithic monthly event, the Google would refresh some of its index pretty much every day, which generated much smaller day-to-day changes that some people called “everflux”.

Over the years, Google’s indexing has been streamlined, to the point where most regular people don’t even notice the index updating. As a result, the terms “everflux,” “Google Dance,” and “index update” are hardly ever used anymore (or they’re used incorrectly ). Instead, most SEOs talk about algorithm updates or data updates/refreshes. Most data refreshes are index updates, although occasionally a data refresh will happen outside of the day-to-day index updates. For example, updated backlinks and PageRanks are made visible every 3-4 months.

What you need to take away from this is that an index update is a type of data refresh. Don’t get hung up on “update” vs. “refresh” since they’re basically the same thing. There’s algorithms, and the data that the algorithms work on. A large part of changing data is the index being updated.

Read Matt Cutts’ statements on the “algorithm update that never happened.”