Motherboard

Motherboard

The best way to describe the motherboard goes along well with my human body analogy that I used for the CPU.  The CPU is the brain, and the motherboard is the nervous system. Therefore, just as a person would want to have fast communication to the body parts, you want fast communication between the parts of your computer.  Fast communication isn't as important as reliable communication though.  If your brain wanted to move your arm, you want to be sure the nervous system can accurately and consistently carry the signals to do that!  Thus, in my opinion, the motherboard is the second most important part of the computer.  
The motherboard is the circuit board to which all the other components of the computer connect in some way.  The video card, sound card, IDE hard drive, etc. all plug into the motherboard's various slots and connectors.  The CPU also plugs into the motherboard via a Socket or a Slot.