CPU, which is often called just "processor", is an abbreviation for Central Processing Unit. That's the core of each laptop or computer or hosting server, since it carries out all of the calculations and logical input/output procedures. Although the performance of a website or an app depends on other things too, like the amount of physical memory or the connection of the web server, the rate at which a given processor works determines how soon an app will be executed. Later-generation processors have a number of cores which can drastically boost their overall power and efficiency, due to the fact that each core can take care of a variety of processes individually or a number of cores can control 1 process which needs a significant processing power. Since each core works at a specific speed, this architecture can be viewed as a number of separate processors cooperating.