The terahertz, abbreviated THz, is a unit of electromagnetic (EM) wave frequency equal to one trillion hertz (1012 Hz). The terahertz is used as an indicator of the frequency of infrared (IR), visible, and ultraviolet (UV) radiation.
An EM wave having a frequency of 1 THz has a wavelength of 0.3 millimeters (mm), or 300 micrometers (?). An EM wave of 540 THz is in the middle of the visible-light spectrum. Wireless transmissions and computer clock speeds are at frequencies far below 1 THz.
The terahertz is not commonly used in computer and wireless technology, although it is possible that a microprocessor with a clock speed of 1 THz might someday be developed. At present, the terahertz is of interest primarily to physicists and astronomers. More commonly-used units of frequency are the kilohertz (kHz), equal to 1,000 Hz or 10-9 THz, the megahertz (MHz), equal to 106 Hz or 10-6 THz, and the gigahertz (GHz), equal to 109 Hz or 0.001 THz.
http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci752929,00.html
I couldn't care less what your pop-science website says. Read a single paper in a scientific journal and you'll see the proper definition. If, say, 500GHz is not in the field of THz technologies, then is it microwave? Infra-red? What?
Take millimetre-wave radar: does millimetre-wave radar operate at other wavelengths, or only one millimetre? If the wavelength is half a millimetre... is it no longer millimetre-wave radar?
THz, in addition to being 10^12 hertz, is also the name of a band of frequencies in the spectrum. It lies above microwave, and below infra-red. They should have called the band 'quasi-optical', but they didn't: they called it the terahertz band.
Andrew