the main interconnecting circuit board in an electronic device, into or on which the various subassemblies, as printed circuit boards, are plugged or wired
See motherboard in American Heritage Dictionary 4
(mŭÞˈər-bôrdˌ, -bōrdˌ)
noun
The main board of a computer, usually containing the circuitry for the central processing unit, keyboard, and monitor and often having slots for accepting additional circuitry.