That was the satelite board used to change a regular Pac/Ms. Pac board into "Pacman Plus". I believe you also needed to swap out some roms and eproms.
It came out at a time (1983ish) when a lot of hacks were coming out, so this became an official upgrade (hence the "Authorized" Enhancment Kit) from the company. They put it in a black epoxy casing so that no one could hack it.