from Slew rate wikipedia:
slew rate effect on a square wave: red= desired output, green= actual output
where is the output produced by the amplifier as a function of time t.
Limitations in slew rate capability can give rise to non linear effects in electronic amplifiers. For a sinusoidal waveform not to be subject to slew rate limitation, the slew rate capability (in volts per second) at all points in an amplifier must satisfy the following condition:
where f is the operating frequency, and is the peak amplitude of the waveform.
The slew rate can be measured using a function generator (usually square wave) and oscilloscope. The unit of slew rate is typically V/µs. The slew rate is same for both when feedback is considered or not considered.
Slew rate limiting in amplifiers
There are slight differences between different amplifier designs in how the slewing phenomenon occurs. However, the general principles are the same as in this illustration.