BS is the prefix used to identify ROMs (dumped video game data) which originally appeared on the Satellaview system in Japan. The system was an add on for the Super Famicom which allowed users to download game files from a satellite televsion channel called St GIGA. Often, games were released both on the Satellaview system and as stand alone Game Pak titles. This happened in the case of Cu-On-Pa, so ROM download websites which are complete will usually specify the two different ROMsets as "Cu-On-Pa" and "BS Cu-On-Pa" to avoid confusion. The ROM titles were dumped thanks to some arcane wizardry, but either way, most of them can now be found floating around the Internet.
The BS prefix comes from the alternate name for the Satellaview; the BS-X which is presumably in reference to the Broadcast Satellite of sekicho's above writeup. Previously, all my BS writeups said that Bandai was a company involved in helping Nintendo make the Satellaview but I have it on good authority that although this is a very widespread belief, it is untrue.
yerricde says "BS-X is probably the same thing that the "-X" stands for at the beginning of a PlayStation EXE's header."
There are a very large amount of BS ROMs available, not least because some games were so big that they were released in a number of different parts. The ones which have been noded on E2 are:
If you node some more of these great forgotten games, or you know some that I've missed, please don't hesitate to /msg me.
Additions from:
yerricde
Servo5678
Your name here.