Economic Definition of I. Defined.
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Term I Definition: The standard abbreviation for investment expenditures by the business sector, especially when used in the study of macroeconomics. This abbreviation is most often seen in the aggregate expenditure equation, AE = C + I + G + (X - M), where C, G, and (X - M) represent expenditures by the other three macroeconomic sectors, household, business, and foreign.