Google’s Knowledge Graph is a new technology launched in 2012 for US queries to give better search results for some types of queries. When launched, the Knowledge Graph identified 3.5 Billion facts about 500 Million "objects" or "entities".
Movies, books and music albums
Cities & countries
Well known historical or public figures
Facts about entities are displayed in a knowledge box on the right side of the SERP.
Data sources are mainly Freebase, Wikipedia, the CIA World Factbook and other secondary partners.
Knowledge Graph development may be a source of traffic drop for some websites and of traffic gain for few others.
An example of SERP using Knowledge Graph: