TDM - Time division multiplexing, the simplest form of multiplexing. For example, if 4 channels need to be sent on one multiplex, they are sent as (F=Frame, C=Channel) 1st F 1st C | 1st F 2nd C | 1st F 3rd C | 4th F 1st C | 2nd F 1st C | 2nd F 2nd C | and so on.
TDT - Mandatory data transmitted within SI to synchronise the receiver's internal clock.
Terrestrial Broadcasters - Broadcasters, which transmit through the airwaves from one earthbound aerial to another, eg BBC and ITV
Threshold - The measure of sensitivity of a satellite receiver measured in decibels (db)
Transponder - Components in a satellite that receive, process and re-transmit a signal up from, and back down to Earth. On Astra satellites most stations are allocated one transponder, though a small number of stations share a transponder.
Twin Tuner - A set-top box that can record two channels at once or record one channel whilst watching another channel live.