NOI

Net Operating Income. Gross rental income less vacancy allowance and operating expenses (property tax, insurance, utilities the landlord pays, maintenance, property management), before debt service. The standardized definition lenders and investors use to compare rentals on apples-to-apples terms.

NOI is what feeds cap rate (NOI / property value) and DSCR (NOI / annual debt service). Both are sensitive to how aggressively or conservatively you size operating expenses. A conservative NOI assumes higher vacancy and higher maintenance than the seller's pro forma; that's the right number to underwrite from.