1. Base band signal is a narrow band of frequencies centered around Zero frequency whereas band pass signal is a band of frequencies with a center frequency not necessarily zero (Assume you translated the base band signal to get some other center frequency).
2. Usually for the ease of transmission the Base band signal is translated to higher center frequency, transmission of which is called the pass band transmission.
3. A baseband channel or lowpass channel (or system, or network) is a communication channel that can transfer frequencies that are very near zero. Examples are serial cables and local area networks (LANs), as opposed to passband channels such as radio frequency channels and passband filtered wires of the analog telephone network. Frequency division multiplexing (FDM) allows an analog telephone wire to carry a baseband telephone call, concurrently as one or several carrier-modulated telephone calls. (Wikipedia)