Terahertz (THz) is a unit of measurement for frequencies in the electromagnetic spectrum. One terahertz is equal to one trillion (10¹²) hertz. It lies in the frequency range between gigahertz (GHz) and infrared radiation. The terahertz spectrum typically ranges from about 0.3 terahertz to about 10 terahertz.

Terahertz radiation has several applications in science and technology, including:

1. Spectroscopy: Terahertz spectroscopy allows the study of the interaction of terahertz radiation with matter. This technique is used in chemistry, materials science, and biology to obtain information about the structure and composition of molecules.

2. Imaging: Terahertz radiation can be used for non-invasive imaging of materials and biological tissue. It penetrates many materials, making it attractive for security inspections and medical applications.

3. Communications: terahertz frequencies could be used in wireless communications in the future, as they could provide greater bandwidth and higher data rates than current wireless technologies.

4. Security: terahertz scanners are used in some security applications to detect weapons or dangerous items worn under clothing.

However, terahertz radiation also presents challenges, such as absorption by humidity and short range, which may limit its use in some cases. Nevertheless, terahertz offers great potential for various applications in science and technology due to its unique properties.