Depletion

What Does Depletion Mean?
An accounting term describing the amortization of assets that can be physically reduced.

Investopedia explains Depletion
Unlike depreciation and amortization, which mainly describe the deduction of expenses due to the aging of equipment and property, depletion is the actual physical reduction of natural resources by companies.

For example, coal mines, oil fields and other natural resources are depleted on company accounting statements. This reduction in the quantity of resources is meant to assist in accurately identifying the value of the asset on the balance sheet.