(WARNING: Very old post, may be obsolete.)
I’ll get this question out of the way with as short an answer as I can.
The Satellaview was an add-on for the Super Famicom. Its “Gimmick”? “Satellite Broadcasting”.
The whole package came with the hardware add-on at the bottom as well as it’s BIOs cart, dubbed the “BS-X”, which would plug into the SFC’s cartridge port.
What does that mean? It means data was sent to you from Satellite. The most relatable comparison I can probably think of is to Sega’s USA service “Sega Channel”, which was a similar concept, although that used Cable instead of satellite, and tried more to simulate on-demand programming than a channel per se.
Using the Satellaview, you could download various things into memory packs, including games, news, and magazines. You could also take advantage of the Satellite Audio capabilities to listen to your favorite radio shows, or play special games which made use of live audio broadcasts to enhance the gameplay.
The Satellaview was a cooperative project between Nintendo, whom need no introduction, and St. Giga, a Japanese Satellite Radio service.
Later articles have dug into St. Giga’s history as a Satellite Digital Radio station in the New-Age Ambience genre, although when the Satellaview was released, there was a radical shift towards celebrity and videogame-oriented programming.The Japanese Wikipedia article has more info.