Bird's nest refers to the nest built by the saliva secreted by some swifts of the order Swiftidae and several species of swiftlets of the genus Swiftlet, and mixed with other materials. Also known as swallow vegetables, swallow roots, and swallow vegetables, bird's nests can be divided into two types: "house nests" and "cave nests" according to the place where the nest is built.

Cave swallows have different colors due to the influence of minerals. They are divided into white swallows, yellow swallows and red swallows, while house swallows only have one color: ivory white. Bird's nest is one of the traditional and precious foods that has been eaten in China since the Ming Dynasty. The so-called "blood swallows" on the market are said to be made from artificially bred house swallows through the "guano infection method".