An asset is an expenditure that has utility through multiple future accounting periods. If an expenditure does not have such utility, it is instead considered an expense. For example, a company pays its electrical bill. This expenditure covers something (electricity) that only had utility during the billing period, which is a past period; therefore, it is recorded as an expense. Conversely, the company buys a machine, which it expects to use for the next five years. Since this expenditure has utility through multiple future periods, it is recorded as an asset.
An asset may be depreciated over time, so that its recorded cost gradually declines over its useful life. Alternatively, an asset may be recorded at its full value until such time as it is consumed. An example of the first case is a building, which may be depreciated over many years. An example of the latter case is a prepaid expense, which will be converted to expense as soon as it is consumed. An asset that is longer-term in nature is more likely to be depreciated, while an asset that is shorter-term in nature is more likely to be recorded at its full value and then charged to expense all at once. The one type of asset that is not considered to be consumed and is not depreciated is land. The land asset is presumed to continue in perpetuity.
An asset does not have to be tangible (such as a machine). It can also be intangible, such as a patent or a copyright.
At a less well-defined level, an asset can also mean anything that is of use to a business or individual, or which will yield some return if it is sold or leased.
On the balance sheet of a business, the total of all assets can be calculated by adding together all liabilities and shareholders' equity line items.