We have already seen reports of it rolled out for some users in the recent past. Google has now officially announced addition of knowledge graph to their search engine. This is available for US based users right now.
Knowledge graph is designed to understand the user query and provide direct information related to that keyword collected from different sources. So for example, if you search for Taj Mahal, you get to see a summary about the monument right on the search result page. Google also highlight other possible entities with the name Taj Mahal in case you wanted to learn more about them.
The idea is to understand what the user wants to search for and let him find the information faster.
Google Search with Knowledge Graph is available on desktop, mobile and tablets.