Besides describing the medieval Black Death the term pest is collectively used for animals, which do harm to human beings, cultivated plants or livestock animals by transmitting diseases, by destroying biomass or by competing for food. Therefore, depending on the judgement of society, the term may cover different organisms.

New pests arise with new cultivations. Monocultures, in particular, support the emergence of pest species. Pests are often augmented by climatic changes or extremes (heat, draught).

With regard to nature, the term pest is rarely used, except for damage caused to natural habitats by the introduction of new species by human beings.