CPU, which is frequently called just "processor", is an abbreviation for Central Processing Unit. That's the core of every computer or hosting server, since it executes all of the calculations and logical input/output procedures. Though the performance of a site or an app depends on other things too, such as the amount of physical memory or the connection of the hosting server, the rate at which a certain processor runs determines how soon an application shall be executed. Later-generation processors have several cores that can significantly improve their overall power and efficiency, as every single core can control numerous processes separately or several cores can take on one process which needs a significant processing power. Since every single core operates at a certain speed, this architecture can be seen as a number of independent processors working together.