A standard DE-9, nine-pin male controller plug.  Popularized by the Atari 2600 as a means of connecting controllers and peripherals, it was later adopted by many other consoles/computers in the early 1980s.
<a href="//commons.wikimedia.org/wiki/User:Evan-Amos" title="User:Evan-Amos">Evan-Amos</a>
<span class="int-own-work" lang="en">Own work</span>