A TV station may broadcast several SDTV shows instead of one HDTV show using digital broadcasting. These multiple programs might be designated 117.1, 117.2, etc. (Only one SDTV show fits in a channel using current analog broadcasting.)
Alternatively a cable system may take several single shows from different stations and combine them on one cable channel.
Video on demand occupies channels in the same way as ordinary programs and in the same way a VCR sends the program it is playing (slow motion, rewinding, and all) to an ordinary TV using channel 3 or 4. I would think that the cable box blocks channels that are used for other people's video on demand but apparently your cable box does not block them and some are not scrambled.
Some channels may have private feeds to certain subscribers such as restaurant chains or even for internal (cable company) use for rebroadcast at a later time. This is similar to video on demand where a complete repertoire of shows is custom made in advance. A long time ago (still done now?) FM radio stations could each use one subchannel to send a private feed such as background music (like Muzak) to subscribers such as restaurants and stores.
Video hints:
http://members.aol.com/ajaynejr/video.htm