The American Heritage® Dictionary of the English Language, 4th Edition
n. Whatever food happens to be available for a meal, especially when offered to a guest: Having arrived unannounced for supper, we had to take potluck.
n. A meal at which each guest brings food that is then shared by all. Also called potluck supper.
n. Whatever is available at a particular time: The scheduled flight was canceled and passengers had to take potluck on the other airlines.