1. To eliminate animal or protozoan pests or parasites from an infested area or host: Some countries are making efforts at defaunating single-cell organisms that divide within a host organism; such as, those protozoa that cause malaria.
2. To drive off or deplete animal life in an area: A process of defaunating local or global extinctions of large (vertebrate) animals as a result of human processes; such as by, hunting or the depletion of forests when people over populate such areas.

Some areas have been defaunated by excessive deforestation by humans which threatens global biodiversity in some areas of the world.

When some areas are overly defaunated, there are impacts resulting from the loss of key pollinators and seed dispersers by the absence of animals that indirectly affects the ecology of the forests.