The term link velocity refers to the rate at which backlinks to a site are accumulated. This can sometimes be an important SEO factor.
Under normal circumstances, a site that contains good quality content will pick up a steady stream of backlinks. For smaller sites that may average a few per month, for large and very active sites that can be thousands of links per month. Google is believed to monitor the average amount of links to a site that are accumulated over time. This is a controversial issue among SEO companies and link-building companies, but it can raise a red flag when a site that normally picks up 10 or 20 new links per month suddenly picks up thousands of links in a given month.
The red flag draws scrutiny. If the site is engaged in link buying with the intent of artificially raising its PageRank value, that would be a violation of Google’s Webmaster Guidelines, which could result in penalties being applied to the site.
There are situations where a site can legitimately pick up large numbers of backlinks very quickly, such as when a very popular article is published or something about the site goes viral. Anything that draws in large numbers of visitors who find the site to be interesting will also create large numbers of legitimate backlinks from a wide range of different web sites.
The difference between viral linking pattern and an artificial pattern is most often revealed by hyperlink text. If a site owner buys 1000 links that all use the words “gold coins” in the hyperlink text, that would be an easy way to identify an artificial linking pattern. A natural linking pattern would have a wide range of text variation in the hyperlink, such as “gold”, “buy gold here”, “good gold prices”, “gold bullion”, “American Eagle coins”, etc.
The link velocity issue can cut both ways. If a site is steadily picking us a few natural links each month and the link velocity drops off to zero, that can possibly raise a flag that the site and its content is becoming stagnant.
If you are engaging in link building to drive traffic, raise your site’s PageRank or improve rankings, be aware of the link velocity issue. It is usually much better to build links to a site slowly over time, than is is to dump hundreds or thousands of links to a site all at once.