Biological invasion is the process of transferring and establishing species (animals, plants, fungi or microorganisms) outside their natural range of distribution, as a result of human activity, either through intentional or unintentional introduction of the species to a new area, where it can establish itself and spread (reproduce). This can involve reproductive cells, seeds, eggs, or other parts of organisms capable of survival and reproduction. These species are referred to as alien species. Unlike native species, which belong to an area within their typical natural (past or present) range, including changes in distribution due to natural expansion, meaning areas reached by the species on its own without human involvement.

Not all alien species become invasive. Invasive alien species represent a subset of alien species that have established and spread and have a negative impact on nature (native biodiversity, local ecosystems, and species), and may also affect humans (ecosystem functions, natural resources, economic activities, health, and quality of life).