Definition: The monetary value of an asset decreases over time due to use, wear and tear or obsolescence. This decrease is measured as depreciation.
Description: Depreciation, i.e. a decrease in an asset's value, may be caused by a number of other factors as well such as unfavorable market conditions, etc. Machinery, equipment, currency are some examples of assets that are likely to depreciate over a specific period of time. Opposite of depreciation is appreciation which is increase in the value of an asset over a period of time.
Accounting estimates the decrease in value using the information regarding the useful life of the asset. This is useful for estimation of property value for taxation purposes like property tax etc. For such assets like real estate, market and economic conditions are likely to be crucial such as in cases of economic downturn.