As with the other people that have replied to your comment, the term THz is now used to apply to the region of physics between problems that have been solved by RF solutions and problems that have been solved by optical solutions. The set of technologies that are being developed to deal with frequencies between these two are very different from either. I work with 0.1 - 3 THz which is referred to as THz technology because the research methods and available technologies are unique to this domain, so a unique name is used to refer to it.