A crop is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion that is found in many animals, including earthworms, leechs, insects, and birds.
Cropping is used by bees to temporarly store nectar of flowers. When bees "suck" nectar, it is stored in their crop. They can then fly while transporting it.
In a bird's digestive system, the crop is an expanded, muscular pouch near the throat. It is a part of the digestive tract, essentially a part of the esophagus. In adult birds, the crop can produce crop milk to feed newly hatched birds, however, not all birds have a crop. As with most other organisms that has a crop, the crop is used to temporarily store food.