Everflux

Everflux is the constant changing in SERP positions of websites. Google changes it’s algorithms every once in while. These updates are usually noticed on blogs and forums pretty fast. These updates usually dramatically change a websites SERP position and are therefore noticed very easily. Certain small ranking changes can not be caused by mayor algorithm updates. These fluctuations are called Everflux and could be caused by the system Goolge uses to display their results.

Whenever a internet user queries Google their request is sent to certain computer/server depending on the server load at that moment. It is believed that Google uses cheap of-the-shelf computers that manage the search queries differently. This causes the minor changes in SERP positions.
Others think that Google adds a random factor on purpose to make search results more organic and to throw off people trying to decipher their algorithm.