Google recently had the Hummingbird update which was a change in the core search algorithm. Google moved from keyword based searching to concept based searching. It included semantic level analysis in order to find out real answers and searcher's intent behind the user query. I would add comprehensive and fresh content to my site after the Hummingbird update.

Prior to the Hummingbird update, Google had the Penguin update which was a measure to control web spam. Penguin update had penalized websites which had a spammy backlinking profile and returned more semantic results. Semantic results were based on the relationship between words present on the search query. Penguin trusted sites that had original and good content, fresh content, good social media presence and quality organic links.