This is an update that Google is rolling out on April 21st, 2015. If your website is not mobile friendly it will NOT be shown on Google. If you have not heard about this update affecting all websites, watch this introduction. More detailed information about responsive/adaptive and what Mobile Friendly means. Most importantly, how do you know if your current website works well on smartphones, etc., and how to fix your site.
Mobile Friendly In Detail? (Testing your site for free.)
So what is mobile friendly, and how do you test or find out if your site is ready for the new Google Updates.