That is still called "line regulation", but that is a misnomer since the circuit rejects a change in the line, rather than regulates the line.
It can be defied in terms of
-Fractional change in output voltage divided by fractional change in input voltage (e.g., ppm/%)
-Fractional change in output voltage divided by absolute change in input voltage (e.g., ppm/V)
-Absolute change in output voltage divided by absolute change in input voltage (e.g., mV/V)
-etc.
For a valid specification, this measurement must be done with all other parameters, including load current and junction temperature, held constant during the change.