chain length, \(\delta\)
In a chain reaction, the average number of times the closed cycle of reactions (involving the chain-propagating reactions) is repeated. It is equal to the rate of the overall reaction divided by the rate of the initiation reaction.
PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 157 (