A potluck is a communal lunch gathering where each guest or group contributes a different, often homemade dish of food to be shared.
The word pot-luck appears in the 16th century English work of Thomas Nashe, and used to mean "food provided for an unexpected or uninvited guest, the luck of the pot."  The modern execution of a "communal meal, where guests bring their own food," most likely originated in the 1930s during the Depression.
Potluck dinners are events where the attendees bring a dish to a meal. Potluck dinners are often organized by religious or community groups, since they simplify the meal planning and distribute the costs among the participants. Smaller, more informal get-togethers with distributed food preparation may also be called potlucks. The only traditional rule is that each dish be large enough to be shared among a good portion (but not necessarily all) of the anticipated guests. In some cases each participant agrees ahead of time to bring a single course, and the result is a multi-course meal. This agreement rectifies the problem of many participants bringing the same dish. Guests may bring in any form of food, ranging from the main course to desserts.