TSID stands for “transmitting subscriber information.”
It is used in fax machines as a field that shows the information of the fax machine sending a transmission. The term is frequently used along with “CSID” (called subscriber information)
When a fax transmission occurs, TSID is sent along with the fax. TSID contains both the fax machine’s name as well as the phone number where it is connected.
TSID information is often printed on a header on the fax document along with date and time of the transmission.