Depletion refers to the act or process of reducing something in quantity, especially when it is being used up or exhausted. It can also refer to a decrease in the amount of something available due to its consumption or use. Depletion can occur naturally over time through processes such as erosion or weathering, but it can also be caused by human activities such as mining, logging, and oil drilling. In economics, depletion refers to the reduction of a resource that cannot be replenished in a human's lifetime, such as fossil fuels or mineral resources.