a species that, due to direct or indirect human activity, occurs in locations beyond its known historical or potential natural range. Refers to species from another continent, region, ecosystem, or habitat.
A species that has been introduced by human agency (deliberately or otherwise) to an area where it has not occurred in historical times (taken as being since 500 years before present) and which is separate from and lies outside, the area where natural range extension could be expected. The species has become established in the wild and has self-maintaining populations. (Eno et al, 1997).
Same as exotic. Plants that evolved somewhere else, usually Europe and Asia, and were brought to North America. They are often thought of as bad, and many are invasive, but many grow just fine here without dominating habitats.