Speed in computer terminology is often referred to Clock speed. It is the rate at which a CPU is able to perform instructions and is measured in megahertz (MHz), with 1 MHz representing a million clock cycles per second. In CPU architecture, the faster the clock speed the faster the computer. The clock speed determines how many instructions can be executed per second by the processor.
The clock rate is the rate at which a computer performs its most basic operations such as adding two numbers or transferring a value from one processor register to another. It is the fundamental rate in cycles per second and is measured in hertz.
Different makes of the processors on the same computer motherboard may have different clock rates. Usually when referring to a computer, the term "clock rate" is used to refer to the speed of the CPU. 
