A band-pass filter is a device that allows a certain range of frequencies to pass while blocking others, such as RLC oscillator which is an analog band-pass filter. A bandpass filter refers to a filter that can pass a certain range of frequencies without attenuation while reducing other of frequencies to a very low level. This concept is opposite to that of a band-stop filter. 

2. An ideal filter should have a completely flat passband for example, no gain or attenuation within the passband, and all frequencies outside the passband should be completely attenuated. Additionally, the transition outside the pass should occur over a very small frequency range. However, an ideal band-pass filter does not exist in reality. Filters cannot completely attenuate all frequencies outside the desired, especially when there is a range outside the desired passband that is attenuated but not isolated. This is often referred to as the filter's roll-off phenomenon is represented by the attenuation magnitude in dB per decade. Typically, filter designs aim to minimize the roll-off range to make the filter's performance closer to the design However, as the roll-off range becomes smaller, the passband becomes less flat and starts to show "ripples". This effect is particularly noticeable at the edges the passband and is known as the Gibbs phenomenon. 

3. Between the lower cutoff frequency f1 and the higher cutoff frequency f2 is the resonant frequency the filter's gain is highest. The bandwidth of the filter is the difference between f2 and f1.