We can make our sites responsive, which means that the site will re-size and restructure according to the device it is being viewed on. You know when you browse the internet on your smart phone and a site looks teeny tiny and you have to continuously zoom and un-zoom? That means the site is not responsive. A responsive theme is easier to navigate and looks better. This is not the same as a specific mobile site, but a mobile optimised version of your full site.