What is GHz?

Some articles on ghz:

Liquid - Microscopic Properties - Sound Dispersion and Structural Relaxation
... In normal liquids, most of this cross over takes place at frequencies between GHz and THz, sometimes called hypersound ... At sub-GHz frequencies, a normal liquid cannot sustain shear waves the zero-frequency limit of the shear modulus is ... after an external perturbation for this reason, the dispersion step in the GHz..THz region is also called structural relaxation ...