CPU, that is often called just "processor", is an abbreviation for Central Processing Unit. That's the core of any laptop or computer or server, because it performs all the calculations and logical input/output functions. Despite the fact that that the performance of a site or an app is determined by other things too, like the amount of physical memory or the connection of the hosting server, the rate at which a certain processor performs determines how quick a program will be executed. Later-generation processors have numerous cores which can seriously improve their overall power and efficiency, because every single core can take care of several processes individually or a number of cores can handle 1 process that requires a substantial computing power. Due to the fact that each core operates at a specific speed, this architecture can be seen as several individual processors cooperating.