‘Depreciation’ is the reduction in the book value of an asset due to its use over time (‘decline in economic usefulness’) or due to legal framework for taxation reporting. The depreciation is usually calculated taking into account the economic life of the asset, expected value of the asset at the end of its economic life (junk/ scrap value), method of depreciation calculation (straight line method, declining balance, sum of year digits, double declining, etc.), and the defined percentage decline in the value of the asset every year (20%, or 15%, and so on).
The depreciation can either be planned or unplanned.