CPU
Central Processing Unit
The Central Processing Unit or CPU is like a "data pump" it moves digital information from one location to another. When a computer displays information on the screen it moves the data from a location in memory or on a file to a location on the screen.
The number of cycles per second determines how quickly the information can be moved as well as the "word size" this is the number of individual bits that are moved in each cycle.
See a more complete "technical" description on Wikipedia
