A mobile-friendly or responsive website is one that changes based on the screen size of the device. Responsive sites are designed to work the exact same way across different devices. This means that nothing changes or becomes unusable on a computer or mobile device.
Responsive websites react with the user in mind, and enhance usability no matter what the device is. Features like navigation, page structure and content all resize and adapt to suit the device they are being viewed on. Simply put, a mobile-friendly website functions the exact same way regardless of the device.
Globally, over 50% of all Google searches are conducted via mobile devices (and these numbers are growing). Your customers are just as likely to access your site from a smartphone and it is your responsibility to provide them with the best user experience possible. This is what mobile optimization is all about: adapting your site, the design, and your content for optimal performance at various screen sizes and platforms.
Having a mobile-friendly website is also an important consideration for SEO. Google actively promotes responsive websites in their search rankings and demote sites that are not optimized for display on smaller screens.