CPU, that's oftentimes called just "processor", is an abbreviation for Central Processing Unit. This is the core of any PC or hosting server, due to the fact that it executes all of the calculations and logical input/output functions. Even though the performance of a site or an application depends on other things too, including the amount of physical memory or the connectivity of the web server, the rate at which a certain processor runs determines how fast an app will be executed. Later-generation processors have multiple cores which can considerably boost their overall power and efficiency, because each core can take on several processes independently or a few cores can control one process which needs a sizeable processing power. As every core works at a specific speed, this architecture can be seen as several separate processors working together.