When a website is responsive, the layout and/or content responds based on the size of the screen the user is viewing. A responsive website automatically changes to fit the device you’re reading it on. Mobile website design provides an optimal viewing and interaction experience for easy reading and navigation with a minimum of resizing, panning, and scrolling for mobile and tablet devices.
When it comes to mobile website design it is not only important for user experience but also search engines, like Google, as they give more influence to sites that are responsive. A mobile friendly website will be made a preference on mobile searches.