These are resources that are finite and can run out. Examples of depletable resources include:
Some depletable resources are potentially renewable but if consumed quicker than the rate of replenishment then they can become depletable.
For example, for many years fishing in the north sea was sustainable. However, with commercial fishing the fish stocks started to dwindle and it became a depletable resource.
Global warming is placing a strain on many natural resources such as water. Whearas water was once more plentiful, it is more frequently in scarce supply.