Gigahertz, generally abbreviated GHz, refers to frequencies in the billions of cycles per second range. Giga is the standard multiplier for 1 billion, and Hertz is the standard unit for measuring frequencies, expressed as cycles or occurrences per second. One GHz is equivalent to one thousand megahertz (MHz).

GHz is commonly used when discussing computer performance or radio frequencies. In computers, GHz most often refers to the clock speed of the central processing unit, or CPU; the faster the CPU clock can tick, the faster, in general, the computer can process data and instructions. In 2000, Intel and Advanced Micro Devices achieved a marketing and technical milestone by releasing the first CPUs to run at 1 GHz. Speeds have subsequently reached 4 GHz.

In radio communications, GHz is used to define bands of the electromagnetic spectrum. Different bands will be assigned different uses. S-Band, for example, is a band of spectrum between 2 and 4 GHz. Common technologies such as Bluetooth®, wireless internet (WiFi) and cordless telephones operate in the S-Band. L-Band, between 1 and 2 GHz, is used for satellite communications and Global Positioning Systems, or GPS. Other notable bands in the GHz range include Ku and Ka, used by satellites as well as by police radar guns.

Devices transmitting at or near the same GHz can interfere with each other. This is caused by the wave-like nature of radio waves; peaks in one wave can be offset by lows in the other wave, thereby nullifying both waves. The closer in frequency the two signals, the more pronounced the effect. Microwave ovens, for example, can interfere with Internet connections because they emit radiation at the same frequency as that used by WiFi routers. Similarly, Bluetooth® and WiFi compete for the same frequencies, and using them concurrently can affect throughput.

The use of GHz frequencies for communications was made possible by advances in semiconductor technologies. Prior to the widespread use of transistors and high-speed electronics, it was not practical to generate such high frequencies.