A clock cycle, or clock tick, is one increment of the CPU clock, during which the smallest unit of processor activity can be performed. Common clock cycle activities include load, store, and jump operations. These operations are typically performed in a series to complete a calculation, such as adding or subtracting two numbers.
The clock speed of a processor is measured in clock cycles per second, or "hertz." For example, a CPU that completes three billion clock cycles per second has a clock speed of 3,000 megahertz, or 3 gigahertz.