Basically, Everflux refers to the constant change in Google's Search Engine Results Pages (SERPs), while Google constantly scours the web looking for “minty fresh” content, changing their index accordingly.
Google don't update their search engine every three months. As alexvgtb says, Google is constantly collecting data about new pages and refreshing data about existing pages. When they see fit, they modify their 'technology' (i.e. how they crawl, index and rank).