Resource depletion occurs when all of the natural resources in an area, both renewable and non-renewable have been exhausted. Human beings currently use resources far more quickly than they can be replenished.
A good example of resource depletion is the growing use of petroleum, which is a finite resource which takes millions of years to create. At the rate we are using up petroleum we could be facing depletion within the next five generations. With growing population and land degradation we are also facing a situation where the Earth can no longer feed the vast amount of people on the planet.