the pre-agreed estimated value at the end of a leasing period of an item subject to a leasing agreement. Glossary of Business Terms
(1) For sequential-pay CMO structures, a residual tranche is the CMO tranche that receives the excess cash flow that remains after all of the payments due to the holders of other tranches and all of the administrative expenses have been met. When the residual is an accrual bond, it is often called a Z tranche or a Z bond.
(2) In REMIC CMO structures, one class of each issue must be designated as the residual for tax purposes. Some REMIC residuals do not meet the traditional definition of a residual as the last tranche to be retired. American Banker Glossary

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residual re‧sid‧u‧al [rɪˈzɪdʒuəl] adjective ACCOUNTING
1. residual income/​revenue/​assets etc the amount of money or assets left after all taxes or other necessary payments have been made:

• the right to any residual assets on the liquidation of the company

— residual noun [countable] :

• the value of the residual after all fixed claims have been met

2. residual income/​payments money that someone gets because work that they did previously continues to produce income, for example money that a writer or actor gets when their work is broadcast again
— residuals noun [plural] :

• The industry is proposing cuts in residuals for certain television reruns.

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residual UK US /rɪˈzɪdjuəl/ adjective [before noun]
remaining after most of something has gone: »

It's a great project to work on, and will have residual benefits for years to come.

ACCOUNTING used to describe an amount of money that is left after some other payments have been made: »

The $60,000 to complete the project is to come from residual funds.

Financial and business terms. 2012.