What is "edible bird's nest"

Edible \Ed"i*ble\, a. [L. edibilis, fr. edere to eat. See Eat.] Fit to be eaten as food; eatable; esculent; as, edible fishes.
--Bacon. -- n. Anything edible.

Edible bird's nest. See Bird's nest, 2.

Edible crab (Zo["o]l.), any species of crab used as food, esp. the American blue crab ( Callinectes hastatus). See Crab.

Edible frog (Zo["o]l.), the common European frog ( Rana esculenta), used as food.

Edible snail (Zo["o]l.), any snail used as food, esp. Helix pomatia and H. aspersa of Europe.

Edible bird's nests are bird nests created by swiftlets using solidified saliva, which are harvested for human consumption. They are particularly prized in Chinese culture due to their rarity, and supposedly high nutritional value and exquisite flavor. Edible bird's nests are among the most expensive animal products consumed by humans, with an average nest retailing for about $2,500 (US) per kilogramme in Asia. The type or grading of bird's nest depends on the type of bird as well as the diet of the bird. It differs in colour from white to dark brown. The Chinese believe that it promotes good health, especially for the skin. The nests have been used in Chinese cooking for over 400 years, most often as bird's nest soup.