The Pigeon update is not a website-penalizing update like the Panda or Penguin updates, but a change in the way Google’s search engine works.
This update was released on July 24th for English search results in the USA, and was also officially released on December 19th 2014 in England, Canada and Australia. The update reached other countries worldwide on the same date as well, albeit unofficially.
For further reading on this update and its influences click here.
In tests conducted by the ZEFO's team we’ve discovered that this update affected a large percentage of keywords around the world - over 50% of keywords were affected as a result of the update.