Content Delivery Network. In this case it's a repository as it's a single shared source on a single server, hardly a network at the moment.
Two main pieces to almost every site Marvelhawk makes. W3 CSS framework which supplies a majority of the user interface and layout of sites and Font Awesome which is great icon library that I use everywhere.
It also contains javascript libraries and lesser used function libraries
You may use it by simply linkin using the code below, however it's mainly a resource for MarvelHawk sites. I'm not preventing the public from using it as getting a usable mirror of Font Awesome latest isn't easily available and W3 at least for me has proven less than reliable when used directly from their host. This really is only relavent to developers/designers and you shouldn't care IMHO.