Google released an update called Hummingbird in September of 2013. The update shifted the focus of SEO away from direct match phrases towards rich topical discussions. I suspect this was in part due to the shift in search volume to phones, and more specifically, Google’s ability to search from voice requests. Google now understands parts of speech and that one question may relate to a previous question. As an example someone might search “where is the Eiffel tower” and then follow with “how tall is it?” in the old world “how tall is it” would be an exact match phrase, but Google interprets the question in context to the previous question and provides links to pages that discuss the Eiffel tower, not to a page with the text “how tall is it”.
Rand Fishkin of MOZ does a great job of discussion optimizing for topics here: