Accumulated Depreciation is a:

Accumulated Depreciation is classified as a contra asset account. This means that it is linked to an asset account, specifically property, plant, and equipment, but it serves to reduce the total value of that account rather than adding to it. The purpose of accumulated depreciation is to reflect the wear and tear, usage, or obsolescence of an asset over time on the balance sheet.

By accumulating depreciation over the asset's useful life, companies can match the expense of using the asset with the revenues it helps generate, adhering to the matching principle in accounting. This approach provides a more accurate representation of the asset's value. Consequently, if we look at the balance sheet, while the asset remains on the books, the net book value reported is the original cost of the asset minus its accumulated depreciation, thereby showing a reduction in value attributable to usage and age.

Other classifications like asset or equity do not apply here, since accumulated depreciation does not represent a future economic benefit (like an asset would) nor does it signify ownership or value beyond mere reduction in asset cost (which would relate more to equity).