Mobile SEO (Mobile Search Engine Optimization) is the process of affecting the visibility and search ranking of a website or a web page when users search on their mobile and other smart devices.
Starting April 21 2015, Google has been expanding their use of mobile-friendliness as a ranking signal. This change affects mobile searches in all languages worldwide and has a significant impact in users’ search results. In this way, users will find it easier to get relevant, high quality search results that are optimized for their devices.
Consequently, mobile friendliness becomes more and more important for a site.