A responsive design website is one that automatically adjusts to the screen size or device that someone is viewing your website. In the very early days of website design, websites were coded via “html table design”. This method effectively created a grid based website that was then delivered to your computer. This was initially a good way to ensure your website looked the same on different computers and browsers in the 90’s.
From table based design grew pure “html and css” based styling. This removed the clunky chunks of code for specific table cells/regions, instead providing styling information based on either inline styling or via a separate “style sheet” – css stands for cascading style sheets and is an additional file that helps an internet browser render a web page.
Ex table based coders used to code elements in HTML and CSS rather like they used to with tables. This led to very rigid designs. As different screen sizes became popular, and mobile and tablets became available this led to websites that needed to be scrolled in all directions to be seen – or ones that were automatically shrunk so small so as to fit on a screens width.
Again, certain web companies entrenched in the old table based designs then started developing specific alternative websites for different devices such as mobile or tablet. In the very early days this worked to an extent, if you ignored the duplicate content issues with the SEO factor, however the sheer number of devices and screen sizes grew to the point this just wasn’t an option anymore.