An 'asset' in economic theory is an output good which can only be partially consumed (like a portable music player) or input as a factor of production (like a cement mixer) which can only be partially used up in production. The necessary quality for an asset is that value remains after the period of analysis so it can be used as a store of value. As such, financial instruments like corporate bonds and common stocks are assets because they store value for the next period. If the good or factor is used up before the next period, there would be nothing upon which to place a value.