Passband Attenuation
Passband attenuation refers to the maximum signal loss within the passband of the filter which should ideally be zero; i.e., pass band shall not attenuate the signal it passes; it's a unit gain region.
The term ripple is about of alternating gain through the passband for certain filter types yet it's still used even if the passband is not alternating such as a Butterworth filter. In that case the frequency at which the gain reduces to -3dB is the cutoff frequency for a lowpass filter. Or similarly high and low cutoff frequencies for a bandpass filter.