CPU, that is oftentimes called just "processor", is an abbreviation for Central Processing Unit. This is the core of every PC or web server, since it performs all the calculations and logical input/output operations. Although the performance of a site or an app depends on other things as well, like the amount of physical memory or the online connectivity of the server, the pace at which a certain processor operates determines how soon an app shall be executed. Later-generation processors have multiple cores which can severely increase their overall power and efficiency, due to the fact that each and every core can control several processes separately or a few cores can deal with 1 process which requires a considerable computing power. As every core operates at a certain speed, this architecture can be looked at as a few individual processors working together.