The Great Foodening is a major event on Foodcourtia. It happens every twenty (Foodcourtia) years and lasts the same amount of years. However, this time may be different elsewhere, as there is a "time warp thing" involved, according to Sizz-Lorr.
The Foodening is run by the Foodcourtia employees who get paid (save for Zim). All employees working on Foodcourtia are stuck on the planet for the entire duration of the Foodening. Because of all the customers swarming to the snacking planet, the gravity is so dense that nobody can leave.
The Foodening is first mentioned in "The Frycook What Came from All That Space" as Sizz-Lorr explains that he was stuck helpless and having to do the work alone on Foodcourtia during the Foodening without Zim to help him. The Fry Lord also has to spend an additional Foodening alone when Zim escapes yet again.
The term "Foodening" was also used as a common noun in the unfinished episode "Return of Keef", implying that "foodening" is a common word in the Irken language that is defined as a gathering of people coming together to eat, like a feast.