That would be a video or graphics adaptor or simply, card.
video
If the CPU is running, but the monitor has no signal, there could be an issue with the cable that connects the CPU to the monitor. There could also be a problem with the VGA card, or the RAM.
A midi is an adapter card that connects to musical instruments.
It is a Sound Card
Look for where you plug in your monitor after opening the case. You'll see 1 of 2 things. 1. Either a large card plugged into a slot perpendicular to the motherboard 2. A cable running from the port you plug the monitor in that connects directly to the motherboard (if this is the case you have what is called an "integrated graphics processor")
You can go to the following website to learn more about what exactly a dual monitor card does and where to get one http://www.nextag.com/dual-monitor-card/stores-html
Which type of monitor? Which type of monitor?
No, a monitor is your computer screen.
HAHJA. Monitor.
HDMI
a card you plug into an electronic device that connects to wifi.
These days, an HDMI interface is used.