APC, which is an acronym for Alternative PHP Cache, is a framework used for caching the compiled source code of a script application, which can speed up a database-driven website several times. Each time a PHP webpage is accessed, the script pulls the website content which has to be shown from a database, parses and compiles the program code, then the result is shown to the website visitor. While this is necessary for sites with regularly changing content, it's a total waste of processing time and resources for an Internet site that doesn't change, for instance an informational portal which displays the same content on a regular basis. As soon as the web pages for such an Internet site are compiled, APC caches them and delivers them every time a website visitor accesses them. Since this saves the time to obtain content from the database and to parse and compile the code, the Internet site will load a lot faster. APC is really useful in particular for scripts with massive source code.