APC, or Alternative PHP Cache, is a PHP module which caches the output code of database-driven script software apps. Dynamic PHP sites keep their content in a database which is accessed whenever a visitor opens a webpage. The content which needs to be displayed is gathered and the code is parsed and compiled before it is delivered to the site visitor. These actions take some processing time and require reading and writing on the hosting server for every single page which is opened. While this can't be avoided for Internet sites with constantly changing content, there're many websites which offer the exact same content on a lot of of their webpages at all times - blogs, informational portals, hotel and restaurant websites, and many others. APC is quite useful for this type of sites since it caches the already compiled code and displays it whenever visitors browse the cached pages, so the code doesn't need to be parsed and compiled all over again. Not only will this reduce the server load, but it will also increase the speed of any site a few times.