Well, its seems to be a standard 8 pin mini din port, apparently - if its a sun or apple device, it might be a serial port - it looks identical to the passthrough port on my sun model 5c keyboard .
If it had 7 pins, i'd guess it was a firewire port, since that looks like an old macbook, but the shape is wrong.
Been searching around, and from I've gathered, it appears to be some sort of ethernet port. Though it is nowhere mentioned explicitly
But then in another source, it is a general term for input devices (Link PDF)
A lot of video cards have a port like this that is for attaching a Composite/Component breakout box dongle. This is a picture of one of the connector, but I have one at home on a 9800 GTX+ that has a different pin layout. This image is from 2004, so the pin layout has probably changed since then.