An organism that cannot synthesize its food from inorganic sources and hence obtains nutrition by feeding on other organisms or organic matter. All heterotrophs are referred to as consumers.
The term consumer applies to any organism in most trophic levels in a food chain, except for producers and decomposers. Consumers include animals and heterotrophic bacteria and fungi. Some plants are carnivorous and therefore consume organic matter. Such plants are regarded as both consumers and producers.
In a food chain, consumers are broadly classified into three levels: Primary, secondary and tertiary. Herbivores that feed on producers are identified as primary consumers. Secondary consumers on primary consumers and/or producers. Tertiary consumers feed on secondary/primary consumers, as well as on producers.