An introduced species (alien species, exotic species, non-indigenous species, or non-native species) is a
The effects of introduced species on natural environments have gained much scrutiny from scientists, governments, farmers and others.
The formal definition of an introduced species, from the
There are many terms associated with introduced species that represent subsets of introduced species, and the terminology associated with introduced species is now in flux for various reasons. Examples of these terms are acclimatized,
General description of introduced species:
In the broadest and most widely used sense, an introduced species is synonymous with non-native and therefore applies as well to most garden and farm organisms; these adequately fit the basic definition given above. However, some sources add to that basic definition "and are now reproducing in the wild",  which removes from consideration as introduced species that were raised or grown in gardens or farms that do not survive without tending by people. With respect to plants, these latter are in this case defined as either ornamental or cultivated plants.
Introduction of a species outside its native range is all that is required to be qualified as an "introduced species" such that one can distinguish between introduced species that may not occur except in cultivation, under domestication or captivity whereas others become established outside their native range and reproduce without human assistance. Such species might be termed "naturalized", "established", "wild non-native species". If they further spread beyond the place of introduction and cause damage to nearby species, they are called "invasive". The transition from introduction, to establishment and to invasion has been described in the context of plants.  Introduced species are essentially "non-native" species. Invasive species are those introduced species that spreadwidely or quickly and cause harm, be that to the environment,  human health, other valued resources or the economy. There have been calls from scientists to consider a species "invasive" only in terms of their spread and reproduction rather than the harm they may cause. 
According to a practical definition, an
Although some argue that "invasive" is a loaded word and harm is difficult to define,  the fact of the matter is that organisms have and continue to be introduced to areas in which they are not native, sometimes with but usually without much regard to the harm that could result.
From a regulatory perspective, it is neither desirable nor practical to list as undesirable or outright ban all non-native species (although the