Transmat was a type of matter/energy conversion techology used by the Ardanan culture on planet Ardana. It was similar to, but distinct from, transporter technology of the type used by the United Federation of Planets and its neighboring cultures. It was used primarily for transport between the Cloud City of Stratos and the planet surface.
During the Great Disruption on Ardana in the late 23rd century, Troglyte rebels were able to seize control of the Stratos City Dwellers' transmat system and invade the city. Following the overthrow of the government and abandonment Stratos, the system lay unused for decades, and eventually ceased functioning.
The transmat system was severely damaged during the Borg Invasion of 2381. Chief Rupi Yee of the USS Sugihara was assigned to supervise the repair of the system, which proved a challenge given its incompatibilities with Federation technology. (ST novel: A Singular Destiny)
- Though the Ardanan's unique technology was seen in TOS episode: "The Cloud Minders", the term "transmat" is used only in Signs from Heaven. This may have been intended as a "tip of the hat" to Doctor Who, as the term was often used in that universe for devices that transmitted matter.