When in a
chain reaction there is a net increase in the number of
chain carriers there is said to be chain branching. A simple example of a
chain-propagating reaction leading to chain branching is:
in which there is one
chain carrier (an oxygen atom) on the left and two chain carriers (a hydrogen atom and a hydroxyl radical) on the right.
Source:
PAC, 1996, 68, 149
(A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996))
on page 156
