CPU, which is oftentimes called just "processor", is an abbreviation for Central Processing Unit. That's the core of each and every personal computer or server, because it carries out all the calculations and logical input/output procedures. Though the performance of a website or an app relies on other things too, including the amount of physical memory or the connection of the server, the pace at which a particular processor performs determines how quick an application shall be executed. Later-generation processors have several cores that can drastically increase their overall power and efficiency, because every core can take on several processes independently or several cores can handle 1 process that needs a significant computing power. Since every single core functions at a particular speed, this architecture can be seen as a number of separate processors cooperating.