A BBQ party where food is cooked based on the timing of guests' arrival. The raw and marinated food is laid out, and as guest arrive they throw whatever they like on the grill and cook it till it is ready to eat. This way the food does not get cold, and the party host is not responsible for "manning" the grill.
Hence the term "Korean" - just like in Korean BBQ restaurants where the raw meat is cooked at the table per the patrons liking.
Person 1: AYO! Am I late for the BBQ? How come the food is not cooked?
Person 2: Allister's having a Korean Cookout foo. The food is on the table. Go cook your own food.
Person 1: Aww Yeah self-service!