BandPass Signal Vs PassBand Signal
A PassBand is the Band that can be passed through a BandPass filter, or for that matter, any filter. In other words, the filter is a Bandpass, what signal passes through is a Passband.
The classic is a high pass and low pass together. For instance, a capacitor, inductor, and resistor in series is an example of a bandpass filter. Digitally, you combine a high pass and a low pass filter together. 
Essentially, if you are limited to a small region, you can infer what frequency you are limited to. The classic example is Nf->2*Nf. The frequencies reported at 0 is 2*Nf, the frequency reported at Nf is actually NF, and continue the pattern for the rest. This only works when you are guaranteed to only have frequencies in the particular band.