Definitions of residual income on the Web:

• Passive income is a rent received on a regular basis, with little effort required to maintain it.
  en.wikipedia.org/wiki/Residual_income

• The excess of controllable operating income over a "minimum" amount of desired controllable operating income.
  www.crfonline.org/orc/glossary/r.html

• The amount of profit that a segment has made after charging a notional amount of interest based on the business’s investment in that segment.
  wps.pearsoned.co.uk/wps/media/objects/1065/1090612/glossary.html

• The net operating income that an investment centre earns above the required return on its operating assets.
  www.mcgrawhill.ca/college/garrison5/student/olc/5mag_gloss_12.html

• The amount of money left over after you have paid all of your ordinary and necessary debts including the mortgage. This calculation is used with VA loans.
  www.crossroadsappraisals.com/terminology.htm

• Net profit less a charge for capital employed.
  cbpc.blog.co.in/2008/11/12/glossary/