What is a processor clock speed?

Answer 1

Here is a short explanation.

Clock rate or clock speed is the speed at which a microprocessor (CPU) executes instructions. Clock speeds are typically expressed in megahertz (MHz) or gigahertz ((GHz). A single clock cycle (usually shorter than a nanosecond in modern non-embedded microprocessors) toggles between a logical zero and a logical one state.

Sources:

http://www.webopedia.com/TERM/C/clock_speed.html

http://en.wikipedia.org/wiki/Clock_rate

Answer 2

Clock Speed is a measurement of the number of cycles per second of a computers synchronisation clock, measured in hertz/Hz (Millions of cycles per second) or gigahertz/GHz (billions of cycles per second).

Older processors tend to perform one instruction (for example 5+3) per clock cycle. So an older 1Hz CPU could perform 1 million instructions per second.

Modern processors are capable perform many instructions in a single cycle. This means that Clock Speed is generally not a very good indicator of a CPUs overall performance.