A chemical reaction for which the expression for the rate of disappearance of a reactant (or rate of appearance of a product) involves rate constants of more than a single elementary reaction. Examples are 'opposing reactions' (where rate constants of two opposed chemical reactions are involved), 'parallel reactions' (for which the rate of disappearance of any reactant is governed by the rate constants relating to several simultaneous reactions to form different respective products from a single set of reactants), and stepwise reactions.
Sources:
PAC, 1993, 65, 2291. 'Nomenclature of kinetic methods of analysis (IUPAC Recommendations 1993)' on page 2293 (https://doi.org/10.1351/pac199365102291)
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1098 (https://doi.org/10.1351/pac199466051077)