Absolute limits of variation in loss through the passband of the filter. Includes ripple, slope, and rolloff at band edges.
The variation in attenuation or gain at a given bias level over the frequency band of interest.
A term expressed in dB to specify the consistent amplitude of a signal spanning a frequency range. Typical expressions: Flatness is to be +/-1dB across (frequency range), OR Flatness shall have 1.5dB peak to peak.