With op-amps (or any other amplifier/driver) there is a speed limit on how quickly the output voltage can change. This speed limit, measured in volts per second (or more commonly, volts per microsecond), is called the slew rate.
The rate of change of the output voltage of an op-amp in response to a step input.
Electronic Devices : Conventional Current Version, 9th Edition by Thomas L. Floyd
Maximum rate at which amplifier output can change in volts per microsecond (V/µs).
Electronic Devices and Circuit Theory, 11th Edition by Robert L. Boylestad & Louis Nashelsky
An op-amp specification indicating the maximum rate at which the output voltage can change. Slew rate is specified in V/µs.
Grob’s Basic Electronics, 11th Edition by Mitchel E. Schultz