Depreciation is an accounting method of allocating the cost of a tangible asset over its useful life and is used to account for declines in value over time. Businesses depreciate long-term assets for both tax and accounting purposes. For tax purposes, businesses can deduct the cost of the tangible assets they purchase as business expenses; however, businesses must depreciate these assets in accordance with IRS rules about how and when the deduction may be taken.


Source : Investopedia