Desert East of Birdsville, Australia. Australia has a very small population because it's land cannot provide enough food to support a larger population.

Overpopulation means that the population of a place is too high. Specifically, there are too many organisms of a certain species in a habitat, so the number of organisms living there is larger than the carrying capacity of the habitat. The habitat cannot support these numbers over time without hurting itself.

The term "overpopulation" is most often used to refer to the number of humans living on Earth.