A festival, gathering, or activity.
[From German Fest, festival.]
This ending was first used by German immigrants to the United States, on the model of words such as Octoberfest for the Munich beer festival, and is still most common there.
Early examples were gabfest, a gathering at which there is a lot of conversation (from gab, speech, as in gift of the gab); songfest, an informal or spontaneous gathering at which people sing; and slugfest, a tough and challenging contest, especially in boxing or baseball.
More recent creations include gloomfest, any unhappy gathering; campfest, a celebration by gays; and rockfest, a rock festival. The sense of activity is often broadly interpreted: gorefest, a type of excessively bloodthirsty film; flamefest, a bout of insults (‘flames’) exchanged between individuals online.