What Is the Meaning of "Depreciation

What is the meaning of "depreciation"?

A) The estimated amount that an entity would currently obtain from disposal of the asset, after deducting disposal costs, for an asset of similar age and condition expected at the end of its useful life.
B) The total amount to be expensed.
C) The systematic allocation of an asset's depreciable amount over its estimated useful life.
D) The estimated period of time over which an asset is expected to be available for use by an entity.