CPU, that's often called just "processor", is an abbreviation for Central Processing Unit. This is the core of each laptop or computer or hosting server, due to the fact that it runs all the calculations and logical input/output operations. Though the performance of a site or an app relies on other things as well, such as the amount of physical memory or the connection of the hosting server, the rate at which a specific processor works determines how quickly an application shall be executed. Later-generation processors have several cores which can drastically improve their overall power and efficiency, because every single core can take care of a number of processes individually or a number of cores can deal with a single process that needs a substantial computing power. As every core functions at a certain speed, this architecture can be looked at as several independent processors working together.