Wiktionary
n. The risk left over after safeguards (mitigation strategies) have been implemented.
Wikipedia
The residual risk is the risk or danger of an action or an event, a method or a (technical) process that, although being abreast with science, still conceives these dangers, even if all theoretically possible safety measures would be applied (scientifically conceivable measures); in other words, the amount of risk left over after natural or inherent risks have been reduced by risk controls.
The general formula to calculate residual risk is
residual risk = (inherent risk) − (impact of risk controls)
where the general concept of risk is ( threats × vulnerability) or, alternatively, (severity × probability).
An example of residual risk is given by the use of automotive seat-belts. Installation and use of seat-belts reduces the overall severity and probability of injury in an automotive accident; however, probability of injury remains when in use, that is, a remainder of residual risk.
In the economic context, residual means “the quantity left over at the end of a process; a remainder”
In the property rights model it is the shareholder that holds the residual risk and therefore the residual profit.