E5410 Filter terminology
1. A lowpass filter is a filter that passes low frequencies -- ie., frequencies around w=0 -- and attenuates or rejects higher frequencies.
2. A high pass filter is a filter that passes high frequencies and attenuates frequencies or rejects low ones.
3. A bandpass filter is a filter that passes a band of frequencies and attenuates frequencies BOTH higher and lower than those in the band that is passed.
4. In each case, the cutoff frequencies are the frequencies defining the boundaries between frequencies that are PASSED and frequencies that are REJECTED -- ie., the frequencies in the passband and stopband.