The Collaborative International Dictionary
Sericin \Ser"i*cin\, n. [L. sericus silken.] (Chem.) A gelatinous nitrogenous material extracted from crude silk and other similar fiber by boiling water; -- called also silk gelatin.
Wiktionary
n. A water-soluble glycoprotein that binds the two fibroin filaments of a silk fibre
Wikipedia
Sericin is a protein created by Bombyx mori (silkworms) in the production of silk.
Silk is a fibre produced by the silkworm in production of cocoon. It consists mainly of two proteins, fibroin and sericin. Silk consists of 70-80% of fibroin and 20-30% sericin; fibroin being the structural center of the silk, and sericin being the gum coating the fibres and allowing them to stick to each other.
The chemical composition of sericin is CHNO.