Wiktionary

1. T-ray(Noun)

   Electromagnetic waves with frequencies intermediate between, and sharing properties of both, short radio waves and long IR optical waves. This region is defined variously as between 0.1 - 10 THz, 0.3-3 THz or 0.3-30 THZ.

   Proceedings of the IEEE, Volume 95, Number 8, August 2007, Special issue: T-Ray Imaging, Sensing, & Retection

Origin: The letter T- from TeraHertz (THz).