Basically it's Linux Hosting on steroids.
In recent years it has become quite clear that the standard LAMP stack (Linux, Apache, MySQL, PHP) simply can't cope with the rigours of dynamic shared hostings. We are fortunate that these days there are optimized replacements for most of the distros and software used in creating a Shared Hosting environment and we have taken full advantage of these recent leaps in technological capability. We present you with CloudLinux, Nginx, MariaDB, eAccelerated, and Memcached (or OpCache). ENJOY!