What kind of risk will remain even if all theoretically possible safety measures would be applied?

Residual risk is defined as the remaining level of risk after countermeasures and safeguards have been applied to inherent risk. Even after exhausting all theoretically possible safety measures, some degree of uncertainty and potential loss remains because perfect security is unattainable - this leftover exposure is, by definition, residual risk.

Inherent risk is the level of risk that exists before any controls or mitigations are applied, which is the opposite of what the question describes.

'Impact risk' is not a standard risk management term; impact is a component used to measure the severity of a risk event, not a category of remaining risk.

'Deferred risk' is not a recognized category in standard risk management frameworks such as NIST RMF or ISO 27005.