Selectable Output Control is a technology mandate promoted by movie studios (represented by The Motion Picture Association of America) to curtail early distribution of movies over pay television platforms such as cable, telco and satellite TV. In May 2010, the FCC agreed to let the movie studios have this power.
The MPAA wants to make sure that if you are able to watch the movie at home, you won't copy it and thus possibly not purchase it on DVD, Blu-ray or watch it on video on demand. The studios thus can select which of your content outputs will work, hence "Selectable Output Control". This is not unprecedented, in fact Apple's iTunes Store requires your computer to have a "protected" digital video output.
They have particular concern for the older analog outputs (devices) versus the never digital outputs (devices) as digital content can be easier to protect. Literally it attempts to disable non-secure, analog outputs.
If you bought your HDTV too early, it won't include the HDMI audio/video inputs that "SOC" will require. Or the TV might have not have enough HDMI inputs, requiring you to unplug one video source to watch another.
SOC restrictions will only be allowed for 90 days or until a movie's release on DVD or Blu-ray, whichever comes first.
Studios won't be allowed to institute a proprietary "digital rights management"-compliant connection; instead they'll have to support HDMI.
The FCC is scheduled to do a review of SOC in 2 years from May, 2010.