RGB - Red, Green, Blue. A type of video signal output (usually via a SCART socket), giving a higher quality signal than a composite video signal.
RSL - Restricted Service Licence. A licence to broadcast a low power regional analogue television service.
RST - Running Status Table. There is no requirement that the now-and-next EIT is synchronised with programme junctions. The RST is an optional element of SI which can be used, for example, to start a vcr.