Chain : The sequence or series of connections between an arbitrary set of nodes. There are open chains and closed chains; synonyms for the latter are circuit, loop, and cycle. Chain is a traditional term to describe neural network organization and has been widely used in this sense at least since Foster & Sherrington (1897, p. 979), Barker (1899, pp. 313-320), Schäfer (1900, vol. 2, p. 608).