The unavoidable "Mega" chip on a plate of nachos.
The chip is usually laden with cheese and has a majority of the toppings stuck to it. It can consist of one or many chips fused together.
Someone always has to eat it, however when the plate of nachos is worked down to the motherchip, everybody hesitates to see who will grab it. The person who does usually has to apologize for taking it.
"Sorry guys, but I'm going for the motherchip. You snooze you lose."