A crop (sometimes also called a croup or a craw, ingluvies, or sublingual pouch) is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion. This anatomical structure is found in a wide variety of animals. It has been found in birds, and in invertebrate animals including gastropods (snails and slugs), earthworms, leeches, and insects.
Cropping is used by bees to temporarily store nectar of flowers. When bees "suck" nectar, it is stored in their crops. Other Hymenoptera also use crops to store liquid food. The crop in eusocial insects, such as ants, has specialized to be distensible, and this specialization enables important communication between colonial insects through trophallaxis.  The crop can be found in the foregut of insects. 
In a bird's digestive system, the crop is an expanded, muscular pouch near the gullet or throat. It is a part of the digestive tract, essentially an enlarged part of the esophagus. As with most other organisms that have a crop, it is used to temporarily store food. Not all bird species have one. In adult doves and pigeons, it can produce crop milk to feed newly hatched birds.
Scavenging birds, such as vultures, will gorge themselves when prey is abundant, causing their crop to bulge. They subsequently sit, sleepy or half torpid, to digest their food.
Most raptors, including hawks, eagles and vultures (as stated above), have a crop; however, owls do not. Similarly, all true quail (Old World quail and New World quail) have a crop, but buttonquail do not. While chickens and turkeys possess a crop, geese do not have one.
Some extinct birds like Enantiornithes didn't have crops.
In the Sherlock Holmes story "The Adventure of the Blue Carbuncle" (1892), author Arthur Conan Doyle hid a valuable gem inside a goose's crop. Unfamiliar with anserine anatomy, Doyle was not aware that geese do not have crops.