DE-9
From Sega Retro
A D-shaped connector with two rows totaling 9 pins. The top row has 5 pins, and the bottom row has 4 pins. Due to the fact that it is a serial port, transmission is done one bit at a time. DB-9 ports are commonly seen on PCs as RS-232C serial ports. They are also used on the Sega Genesis for connecting input devices, such as joypads. (Earlier revisions of the Sega Genesis had a third DB-9 port on the back of the console for a modem adapter.)
Two types of DB-9 connectors exist. A male DB-9 connector has pins, while a female DB-9 connector has holes. You can only plug a male connector into a female plug or vice versa, unless you have a DB-9 gender changer.
Images
This is a male DB-9 connector: http://database.ssonicnet.com/images/DB-9m.png
This is a female DB-9 connector: http://database.ssonicnet.com/images/DB-9f2.png