From MythTV

column sourceid

The Video Source is MythTV's descriptive term for a collection of channels. If you get, say, analog cable from the local cable company, have a broadcast antenna, and have a Dish Network satellite tuner, each of these is a separate Video Source. Each Video Source has a sourceid, an arbitrary sequential integer.

It's a term similar to "channel lineup", often used by program data source services like Data Direct to describe the list of channels you can get in a given area, or via a specific technology.

A given program source -- like CNN, for example -- may appear on different channels on different Video Sources. As long as the program data services all use the same callsign, MythTV will realize that the different channels are all the same program, and can use this informatio to reassign recordings. If the sources use different callsigns, this can be fixed by modifying.