The Genesis Speakers (for lack of a better name) are a simple pair of speakers with Sega Genesis branding.
The speakers were not sold in stores, instead given away in late 1990 and early 1991 to North American customers who had purchased three Mega Drive games between 26th December 1990 and 28th February 1991. At the time, it was not uncommon for televisions to only output sound through one speaker (i.e. they are monaural), and likewise, the original model Mega Drive can only output stereo sound via its built-in headphone socket. The idea, then, was that if these speakers were plugged in to a Mega Drive console, users could experience better quality sound with their games.
Today stereo speakers are commonplace, are built into most televisions and have been superseded in modern consoles by various forms of surround sound setups. The redesigned Mega Drive 2 console also outputs stereo to the television (and lacks a headphone socket), removing the need for these peripherals to exist. The speakers themselves are not Mega Drive-specific, however they command slightly higher prices second-hand for their novelty value.