NOI (Net Operating Income) is a metric that measures the net operating income of a property or investment portfolio before accounting for interest, taxes, depreciation, and amortization. It is calculated as the difference between the total income generated by the property (e.g., rent) and the operating expenses (e.g., maintenance, management). NOI provides an overview of the profitability and efficiency of operating the property and is an important indicator when evaluating its investment performance.