A Responsive Website is a website created using Responsive Web Design (RWD).  A website design using RWD Techniques will adapt to optimally display on the device that it is being rendered on.  So if you hit the website using an iPhone it will display in the best way it can on your iPhone and adapt to whether you hold the phone vertically or horizontally. Responsive websites are optimized to display content on smartphones, tablets, laptops, and desktop computers as well as to adapt to a user turning their phone or tablet sideways.  They are also optimized to work well on touch enabled devices such as mobile phones and tablets.  Traditional websites were created for people to click on things using a mouse, while modern websites are created to not only allow clicks and for people to touch their way through on a smartphone or tablet, but also to encourage users to take action.

The reason that you need a responsive website is that over 36% of mobile subscribers are using iPhones or iPads to read emails and 34% only use mobile devices to read their emails. If you are using the power of sending emails to encourage business, then you are sending them to a lot of phones and tablets.  So, when a phone or tablet user clicks on a link to your website, they are going to view the website on their phone or tablet, and not on a computer.  Over 80% of internet users now own a smartphone. Another key factor is that that for effective SEO allowing your website to be found on search engines like Google, then you have to be mobile-friendly.