Custard is a liquid that is thickened or set by the coagulation of egg protein.
There are two basic kinds of custard:
Stirred custard, which is stirred as it cooks and remains pourable when done.
Baked custard, which is not stirred and sets firm.
One basic rule governs the preparation of both custards: Do not heat custards higher than an internal temperature of 185ºF (85ºC).
Quiche is a custard baked in a pastry shell.