Google has been progressively rolling out some major changes and updates over the past two or so years. Last year Google debuted The Knowledge Graph, which is an extensive database of the most searched for people, places, and things. This year came Hummingbird, which was designed to provide users with better results based upon how you search, rather than from keywords used. These changes all result from a new search approach for Google.
Semantic search
Until recently, Google has primarily relied on keywords and phrases to provide users with links to their search results. This is no longer the way with semantic search.
Semantic search draws upon the use of language and the relationships between words used in a search in order to provide answers. It means to be an improvement of search accuracy by understanding user intent. When you search, Google will know right away what you're referring to and give you the answer by drawing upon its extensive knowledge database. It is Googles road to understanding conversational language used in searches.
Google is leveraging everything it knows about a searcher in order to provide semantic search results. Things such as device type, location, and search habits will all influence what Google presumes to be the user's intent when performing a search. As the use of semantic search goes on, you are providing Google the entity information it needs for its Knowledge Graph.
Knowledge Graph
The Knowledge Graph is used to provide facts about people, places, and things in conjunction with Google's traditional results. It's Google's term for how it is building relationships between people places and things to report facts about them. The aim is to garner information from an extensive range of sources to make your search results more accurate.
Through the graph, Google is attempting to understand the query and establish associative context around the entities. Basically, the knowledge graph is aimed to produce answers not just links. It will help users get what they need without having to navigate through various websites to compile the information they get on their own.
Does it effect SEO?
So far, Keywords were easy to work with in the sense that you could optimize your site around them. Optimizing your site around the intent of users will be a little more challenging. Google hasn't explicitly stated whether or not there would be an impact on SEO; but know that when people perform a search they are looking for answers. They want personalized information at their fingertips.
Essentially you will need to write for human users and not search engines. With everything that you write ask yourself if it helps answer the searchers question. Good SEO goes beyond the reliance of your keywords. It is no secret that Google appreciates sites that provide original, well written, and original content.