From AMS Glossary
(Also called bred modes.) Perturbations generated by the breeding method.
In complex physical systems the bred vectors depend on the perturbation amplitude, which is the only free parameter in the breeding technique. For example, linearly fast-growing perturbations such as convective instabilities do not amplify after reaching a certain amplitude since they become nonlinearly saturated (i.e., other processes prevent them from growing any further). The bred vectors are primarily used as initial perturbations in ensemble forecasting and for studying the instabilities of the atmosphere.