Vermin is a term applied to various animal species regarded as pests or nuisances and especially to those associated with the carrying of disease. Since the term is defined in relation to human activities, which species are included will vary from area to area and even person to person. The term itself derives from the Latin vermis, meaning worm, and originally had reference to the vermiform larvae of certain insects, many of which infest foodstuffs. Disease-carrying rodents and insects are the usual case, but the term is also applied to larger animals, on the basis that they exist out of balance with a desired environment, consuming excessive resources. Pigeons, which have been widely introduced in urban environments, may be considered vermin, or, pejoratively, "flying rats." Some varieties of snake are also referred to as vermin from time to time.
The term is also used as an extremely pejorative characterization of a particular class or group of people as inferior and subhuman, and often considered social parasites. Application of the term can be wide, having been applied over the centuries in different languages, to various groups, and its use is usually based on a perception that the target group's views are "disease-like," or that such groups exist out of sociological balance with the common society.